OCTOBER TERM, 2000

															Syllabus

															ILLINOIS v. McARTHUR

															CERTIORARI TO THE APPELLATE COURT OF ILLINOIS, FOURTH
DISTRICT

															No. 99-1132. Argued November 1, 2000-Decided February 20,
2001

															Police officers, with probable cause to believe that respondent
McArthur had hidden marijuana in his home, prevented him from
entering the home unaccompanied by an officer for about two hours
while they obtained a search warrant. Once they did so, the
officers found drug paraphernalia and marijuana, and arrested
McArthur. He was subsequently charged with misdemeanor possession
of those items. He moved to suppress the evidence on the ground
that it was the "fruit" of an unlawful police seizure, namely, the
refusal to let him reenter his home unaccompanied. The Illinois
trial court granted the motion, and the State Appellate Court
affirmed. Held: Given the nature of the intrusion and the law
enforcement interest at stake, the brief seizure of the premises
was permissible under the Fourth Amendment. Pp. 330-337.

															(a) The Amendment's central requirement is one of
reasonableness.

															Although, in the ordinary case, personal property seizures are
unreasonable unless accomplished pursuant to a warrant, United
States v. Place, 462 U. S. 696 , 701, there
are exceptions to this rule involving special law enforcement
needs, diminished expectations of privacy, minimal intrusions, and
the like, see, e. g., Pennsylvania v. Labron, 518 U. S. 938 ,
940-941. The circumstances here involve a plausible claim of
specially pressing or urgent law enforcement need. Cf., e. g.,
United States v. Place, supra, at 701. Moreover, the
restraint at issue was tailored to that need, being limited in time
and scope, cf. Terry v. Ohio, 392 U. S. 1, 29-30, and
avoiding significant intrusion into the home itself, cf. Payton v. New York, 445 U. S. 573 , 585.
Consequently, rather than employing a per se rule of
unreasonableness, the Court must balance the privacy-related and
law enforcement-related concerns to determine if the intrusion here
was reasonable. Cf. Delaware v. Prouse, 440 U. S. 648 , 654. In
light of the following circumstances, considered in combination,
the Court concludes that the restriction was reasonable, and hence
lawful. First, the police had probable cause to believe that
McArthur's home contained evidence of a crime and unlawful drugs.
Second, they had good reason to fear that, unless restrained, he
would destroy the drugs before they could return with a warrant.
Third, they 327 made reasonable efforts to reconcile their law enforcement needs
with the demands of personal privacy by avoiding a warrantless
entry or arrest and preventing McArthur only from entering his home
unaccompanied. Fourth, they imposed the restraint for a limited
period, which was no longer than reasonably necessary for them,
acting with diligence, to obtain the warrant. Pp. 330-333.

															(b) The conclusion that the restriction was lawful finds
significant support in this Court's case law. See, e. g.,
Segura v. United States, 468 U. S. 796 ; United
States v. Place, supra, at 706. And in no case has this
Court held unlawful a temporary seizure that was supported by
probable cause and was designed to prevent the loss of evidence
while the police diligently obtained a warrant in a reasonable
period. But cf. Welsh v. Wisconsin, 466 U. S. 740 , 754.
Pp.333-334.

															(c) The Court is not persuaded by the countervailing
considerations raised by the parties or lower courts: that the
police proceeded without probable cause; that, because McArthur was
on his porch, the police order that he stay outside his home
amounted to an impermissible "constructive eviction"; that an
officer, with McArthur's consent, stepped inside the home's doorway
to observe McArthur when McArthur reentered the home on two or
three occasions; and that Welsh v. Wisconsin, supra, at 742, 754, offers direct support for McArthur's position. Pp.
334-336.

															304 Ill. App. 3d 395, 713 N. E. 2d 93, reversed and
remanded.

															BREYER, J., delivered the opinion of the Court, in which
REHNQUIST, C. J., and O'CONNOR, SCALIA, KENNEDY, SOUTER, THOMAS,
and GINSBURG, JJ., joined. SOUTER, J., filed a concurring opinion, post, p. 337. STEVENS, J., filed a dissenting opinion, post, p. 338. Joel D. Bertocchi, Solicitor General of Illinois, argued
the cause for petitioner. With him on the briefs were James E.
Ryan, Attorney General, and William L. Browers and Colleen M. Griffin, Assistant Attorneys General.

															Matthew D. Roberts argued the cause for the United States as
amicus curiae urging reversal. With him on the brief were Solicitor
General Waxman, Assistant Attorney General Robinson, Deputy
Solicitor General Dreeben, and Deborah Watson. 328 Deanne Fortna Jones argued the cause for respondent.

															With her on the brief was Jeff Justice. *

															JUSTICE BREYER delivered the opinion of the Court. Police
officers, with probable cause to believe that a man had hidden
marijuana in his home, prevented that man from entering the home
for about two hours while they obtained a search warrant. We must
decide whether those officers violated the Fourth Amendment. We
conclude that the officers acted reasonably. They did not violate
the Amendment's requirements. And we reverse an Illinois court's
holding to the contrary.

															I A

															On April 2, 1997, Tera McArthur asked two police officers to
accompany her to the trailer where she lived with her husband,
Charles, so that they could keep the peace while she removed her
belongings. The two officers, Assistant Chief John Love and Officer
Richard Skidis, arrived with

															* A brief of amici curiae urging reversal was filed for
the State of Ohio et al. by Betty D. Montgomery, Attorney
General of Ohio, Edward B. Foley, State Solicitor, and Robert C. Maier and Matthew D. Miko, Assistant
Solicitors, and by the Attorneys General for their respective
States as follows: Bruce M. Botelho of Alaska, Janet
Napolitano of Arizona, M. Jane Brady of Delaware, Alan G. Lance of Idaho, Thomas J. Miller of Iowa, Andrew Ketterer of Maine, J. Joseph Curran, Jr., of Maryland, Mike Hatch of
Minnesota, Joseph P. Mazurek of Montana, Philip
McLaughlin of New Hampshire, John J. Farmer, Jr., of New Jersey, Don Stenberg of Nebraska, Frankie Sue Del
Papa of Nevada, W A. Drew Edmondson of Oklahoma, Charles M. Condon of South Carolina, Mark Barnett of
South Dakota, Jan Graham of Utah, William H. Sorrell of Vermont, Christine O. Gregoire of Washington, Thomas F. Reilly of Massachusetts, D. Michael
Fisher of Pennsylvania, and Mark L. Earley of
Virginia.

															Briefs of amici curiae urging affirmance were filed for
the National Association of Criminal Defense Lawyers by Lisa B.
Kemler; and for the Rutherford Institute by John W
Whitehead and Steven H. Aden. 329 Tera at the trailer at about 3:15 p.m. Tera went inside, where
Charles was present. The officers remained outside.

															When Tera emerged after collecting her possessions, she spoke to
Chief Love, who was then on the porch. She suggested he check the
trailer because "Chuck had dope in there." App. 15. She added (in
Love's words) that she had seen Chuck "slid[e] some dope underneath
the couch." Id., at 19.

															Love knocked on the trailer door, told Charles what Tera had
said, and asked for permission to search the trailer, which Charles
denied. Love then sent Officer Skidis with Tera to get a search
warrant.

															Love told Charles, who by this time was also on the porch, that
he could not reenter the trailer unless a police officer
accompanied him. Charles subsequently reentered the trailer two or
three times (to get cigarettes and to make phone calls), and each
time Love stood just inside the door to observe what Charles
did.

															Officer Skidis obtained the warrant by about 5 p.m.

															He returned to the trailer and, along with other officers,
searched it. The officers found under the sofa a marijuana pipe, a
box for marijuana (called a "one-hitter" box), and a small amount
of marijuana. They then arrested Charles.

															B

															Illinois subsequently charged Charles McArthur with unlawfully
possessing drug paraphernalia and marijuana (less than 2.5 grams),
both misdemeanors. See Ill. Compo Stat., ch. 720, §§ 550/4(a),
600/3.5(a) (1998). McArthur moved to suppress the pipe, box, and
marijuana on the ground that they were the "fruit" of an unlawful
police seizure, namely, the refusal to let him reenter the trailer
unaccompanied, which would have permitted him, he said, to "have
destroyed the marijuana." App.27.

															The trial court granted McArthur's suppression motion.

															The Appellate Court of Illinois affirmed, 304 Ill. App. 3d 330 395, 713 N. E. 2d 93 (1999), and the Illinois Supreme Court
denied the State's petition for leave to appeal, 185 Ill. 2d 651,
720 N. E. 2d 1101 (1999). We granted certiorari to determine
whether the Fourth Amendment prohibits the kind of temporary
seizure at issue here.

															II A

															The Fourth Amendment says that the "right of the people to be
secure in their persons, houses, papers, and effects, against
unreasonable searches and seizures, shall not be violated." U. S.
Const., Amdt. 4. Its "central requirement" is one of
reasonableness. See Texas v. Brown, 460 U. S. 730 , 739
(1983). In order to enforce that requirement, this Court has
interpreted the Amendment as establishing rules and presumptions
designed to control conduct of law enforcement officers that may
significantly intrude upon privacy interests. Sometimes those rules
require warrants. We have said, for example, that in "the ordinary
case," seizures of personal property are "unreasonable within the
meaning of the Fourth Amendment," without more, "unless ...
accomplished pursuant to a judicial warrant," issued by a neutral
magistrate after finding probable cause. United States v. Place, 462 U.
S. 696 , 701 (1983).

															We nonetheless have made it clear that there are exceptions to
the warrant requirement. When faced with special law enforcement
needs, diminished expectations of privacy, minimal intrusions, or
the like, the Court has found that certain general, or individual,
circumstances may render a warrantless search or seizure
reasonable. See, e. g., Pennsylvania v. Labron, 518 U. S. 938 ,
940-941 (1996) (per curiam) (search of automobile supported
by probable cause); Michigan Dept. of State Police v. Sitz, 496 U.
S. 444 , 455 (1990) (suspicionless stops at drunk driver
checkpoint); United States v. Place, supra, at 706
(temporary seizure of luggage based on reasonable suspicion); Michigan v. 331 Summers, 452 U. S. 692 , 702-705
(1981) (temporary detention of suspect without arrest warrant to
prevent flight and protect officers while executing search
warrant); Terry v. Ohio, 392 U. S. 1 , 27 (1968)
(temporary stop and limited search for weapons based on reasonable
suspicion).

															In the circumstances of the case before us, we cannot say that
the warrantless seizure was per se unreasonable. It involves
a plausible claim of specially pressing or urgent law enforcement
need, i. e., "exigent circumstances." Cf., e. g., United States v. Place, supra, at 701 ("[T]he
exigencies of the circumstances" may permit temporary seizure
without warrant); Warden, Md. Penitentiary v. Hayden, 387 U. S. 294 ,
298-299 (1967) (warrantless search for suspect and weapons
reasonable where delay posed grave danger); Schmerber v. California, 384 U. S. 757 , 770-771
(1966) (warrantless blood test for alcohol reasonable where delay
would have led to loss of evidence). Moreover, the restraint at
issue was tailored to that need, being limited in time and scope,
cf. Terry v. Ohio, supra, at 29-30, and avoiding
significant intrusion into the home itself, cf. Payton v. New York, 445
U. S. 573 , 585 (1980) (" '[T]he chief evil against which the
... Fourth Amendment is directed' " is warrantless entry and search
of home) (quoting United States v. United States Dist.
Court for Eastern Dist. of Mich., 407 U. S. 297 , 313
(1972)). Consequently, rather than employing a per se rule
of unreasonableness, we balance the privacy-related and law
enforcement-related concerns to determine if the intrusion was
reasonable. Cf. Delaware v. Prouse, 440 U. S. 648 ,654 (1979)
(determining lawfulness by balancing privacy and law enforcement
interests); United States v. BrignoniPonce, 422 U. S. 873 , 878 (1975)
(same).

															We conclude that the restriction at issue was reasonable, and
hence lawful, in light of the following circumstances, which we
consider in combination. First, the police had probable cause to
believe that McArthur's trailer home contained evidence of a crime
and contraband, namely, unlawful 332 drugs. The police had had an opportunity to speak with Tera
McArthur and make at least a very rough assessment of her
reliability. They knew she had had a firsthand opportunity to
observe her husband's behavior, in particular with respect to the
drugs at issue. And they thought, with good reason, that her report
to them reflected that opportunity. Cf. Massachusetts v. Upton, 466 U.
S. 727 , 732-734 (1984) (per curiam) (upholding search
warrant issued in similar circumstances).

															Second, the police had good reason to fear that, unless
restrained, McArthur would destroy the drugs before they could
return with a warrant. They reasonably might have thought that
McArthur realized that his wife knew about his marijuana stash;
observed that she was angry or frightened enough to ask the police
to accompany her; saw that after leaving the trailer she had spoken
with the police; and noticed that she had walked off with one
policeman while leaving the other outside to observe the trailer.
They reasonably could have concluded that McArthur, consequently
suspecting an imminent search, would, if given the chance, get rid
of the drugs fast.

															Third, the police made reasonable efforts to reconcile their law
enforcement needs with the demands of personal privacy. They
neither searched the trailer nor arrested McArthur before obtaining
a warrant. Rather, they imposed a significantly less restrictive
restraint, preventing McArthur only from entering the trailer
unaccompanied. They left his home and his belongings intact-until a
neutral Magistrate, finding probable cause, issued a warrant.

															Fourth, the police imposed the restraint for a limited period of
time, namely, two hours. Cf. Terry v. Ohio, supra, at
28 (manner in which police act is "vital ... part of ... inquiry").
As far as the record reveals, this time period was no longer than
reasonably necessary for the police, acting with diligence, to
obtain the warrant. Compare United 333 States v. Place, 462 U. S., at 709-710 (holding
90-minute detention of luggage unreasonable based on nature of
interference with person's travels and lack of diligence of
police), with United States v. Van Leeuwen, 397 U. S. 249 , 253 (1970)
(holding 29-hour detention of mailed package reasonable given
unavoidable delay in obtaining warrant and minimal nature of
intrusion). Given the nature of the intrusion and the law
enforcement interest at stake, this brief seizure of the premises
was permissible.

															B

															Our conclusion that the restriction was lawful finds significant
support in this Court's case law. In Segura v. United
States, 468 U. S.
796 (1984), the Court considered the admissibility of drugs
which the police had found in a lawful, warrant-based search of an
apartment, but only after unlawfully entering the apartment and
occupying it for 19 hours. The majority held that the drugs were
admissible because, had the police acted lawfully throughout, they
could have discovered and seized the drugs pursuant to the validly
issued warrant. See id., at 799, 814-815 (citing Silverthorne
Lumber Co. v. United States, 251 U. S. 385 (1920)).
The minority disagreed. However, when describing alternative lawful
search and seizure methods, both majority and minority assumed, at
least for argument's sake, that the police, armed with reliable
information that the apartment contained drugs, might lawfully have
sealed the apartment from the outside, restricting entry into the
apartment while waiting for the warrant. Compare Segura v. United States, 468 U. S., at 814 ("Had police never entered
the apartment, but instead conducted a perimeter stakeout to
prevent anyone from entering ... and destroying evidence, the
contraband ... would have been ... seized precisely as it was
here"), with id., at 824, n. 15 (STEVENS, J., dissenting) ("I
assume impoundment would be permissible 334 even absent exigent circumstances when it occurs 'from the
outside' -when the authorities merely seal off premises pending the
issuance of a warrant but do not enter"); see also Mincey v. Arizona, 437
U. S. 385 , 394 (1978) (exigent circumstances do not justify
search where police guard at door could prevent loss of evidence); United States v. Jeffers, 342 U. S. 48 , 52 (1951)
(same).

															In various other circumstances, this Court has upheld temporary
restraints where needed to preserve evidence until police could
obtain a warrant. See, e. g., United States v. Place,
supra, at 706 (reasonable suspicion justifies brief detention
of luggage pending further investigation); United States v. Van Leeuwen, supra, at 253 (reasonable suspicion justifies
detaining package delivered for mailing). Cf. Richards v. Wisconsin, 520
U. S. 385 , 395 (1997) (no need to "knock and announce" when
executing a search warrant where officers reasonably suspect that
evidence might be destroyed); Carroll v. United
States, 267 U. S.
132 , 153 (1925) (warrantless search of automobile
constitutionally permissible ).

															We have found no case in which this Court has held unlawful a
temporary seizure that was supported by probable cause and was
designed to prevent the loss of evidence while the police
diligently obtained a warrant in a reasonable period of time. But
cf. Welsh v. Wisconsin, 466 U. S. 740 , 754 (1984)
(holding warrantless entry into and arrest in home unreasonable
despite possibility that evidence of noncriminal offense would be
lost while warrant was being obtained).

															C

															Nor are we persuaded by the countervailing considerations that
the parties or lower courts have raised. McArthur argues that the
police proceeded without probable cause. But McArthur has waived
this argument. See 304 Ill. App. 3d, at 397, 713 N. E. 2d, at 95
(stating that McArthur 335 does not contest existence of probable cause); Brief in
Opposition 7 (acknowledging probable cause). And, in any event, it
is without merit. See supra, at 331-332.

															The Appellate Court of Illinois concluded that the police could
not order McArthur to stay outside his home because McArthur's
porch, where he stood at the time, was part of his home; hence the
order "amounted to a constructive eviction" of McArthur from his
residence. 304 Ill. App. 3d, at 402, 713 N. E. 2d, at 98. This
Court has held, however, that a person standing in the doorway of a
house is "in a 'public' place," and hence subject to arrest without
a warrant permitting entry of the home. United States v. Santana, 427 U.
S. 38 , 42 (1976). Regardless, we do not believe the difference
to which the Appellate Court points-porch versus, e. g.,
front walk-could make a significant difference here as to the
reasonableness of the police restraint; and that, from the Fourth
Amendment's perspective, is what matters.

															The Appellate Court also found negatively significant the fact
that Chief Love, with McArthur's consent, stepped inside the
trailer's doorway to observe McArthur when McArthur reentered the
trailer on two or three occasions. 304 Ill. App. 3d, at 402-403,
713 N. E. 2d, at 98. McArthur, however, reentered simply for his
own convenience, to make phone calls and to obtain cigarettes.
Under these circumstances, the reasonableness of the greater
restriction (preventing reentry) implies the reasonableness of the
lesser (permitting reentry conditioned on observation).

															Finally, McArthur points to a case (and we believe it is the
only case) that he believes offers direct support, namely, Welsh v. Wisconsin, supra. In Welsh, this
Court held that police could not enter a home without a warrant in
order to prevent the loss of evidence (namely, the defendant's
blood alcohol level) of the "nonjailable traffic offense" of
driving while intoxicated. 466 U. S., at 742, 754. McArthur
notes 336 that his two convictions are for misdemeanors, which, he says,
are as minor, and he adds that the restraint, keeping him out of
his home, was nearly as serious.

															We nonetheless find significant distinctions. The evidence at
issue here was of crimes that were "jailable," not "nonjailable."
See Ill. Compo Stat., ch. 720, § 550/4(a) (1998); ch. 730, §
5/5-8-3(3) (possession of less than 2.5 grams of marijuana
punishable by up to 30 days in jail); ch. 720, § 600/ 3.5; ch. 730,
§ 5/5-8-3(1) (possession of drug paraphernalia punishable by up to
one year in jail). In Welsh, we noted that, "[g]iven that
the classification of state crimes differs widely among the States,
the penalty that may attach to any particular offense seems to
provide the clearest and most consistent indication of the State's
interest in arresting individuals suspected of committing that
offense." 466 U. S., at 754, n. 14. The same reasoning applies
here, where class C misdemeanors include such widely diverse
offenses as drag racing, drinking alcohol in a railroad car or on a
railroad platform, bribery by a candidate for public office, and
assault. See, e. g., Ill. Compo Stat., ch. 65, § 5/4-8-2
(1998); ch. 610, § 90/1; ch. 625, § 5/11-504; ch. 720, §
5/12-l.

															And the restriction at issue here is less serious. Temporarily
keeping a person from entering his home, a consequence whenever
police stop a person on the street, is considerably less intrusive
than police entry into the home itself in order to make a
warrantless arrest or conduct a search. Cf. Payton v. New
York, 445 U. S., at 585 (the Fourth Amendment's central concern
is the warrantless entry and search of the home).

															We have explained above why we believe that the need to preserve
evidence of a "jailable" offense was sufficiently urgent or
pressing to justify the restriction upon entry that the police
imposed. We need not decide whether the circumstances before us
would have justified a greater restriction for this type of offense
or the same restriction were only a "nonjailable" offense at
issue. 337 III

															In sum, the police officers in this case had probable cause to
believe that a home contained contraband, which was evidence of a
crime. They reasonably believed that the home's resident, if left
free of any restraint, would destroy that evidence. And they
imposed a restraint that was both limited and tailored reasonably
to secure law enforcement needs while protecting privacy interests.
In our view, the restraint met the Fourth Amendment's demands.

															The judgment of the Illinois Appellate Court is reversed, and
the case is remanded for further proceedings not inconsistent with
this opinion.

															It is so ordered.

															JUSTICE SOUTER, concurring.

															I join the Court's opinion subject to this afterword on two
points: the constitutionality of a greater intrusion than the one
here and the permissibility of choosing impoundment over immediate
search. Respondent McArthur's location made the difference between
the exigency that justified temporarily barring him from his own
dwelling and circumstances that would have supported a greater
interference with his privacy and property. As long as he was
inside his trailer, the police had probable cause to believe that
he had illegal drugs stashed as his wife had reported and that with
any sense he would flush them down the drain before the police
could get a warrant to enter and search. This probability of
destruction in anticipation of a warrant exemplifies the kind of
present risk that undergirds the accepted exigent circumstances
exception to the general warrant requirement. Schmerber v. California, 384 U. S. 757 , 770-771
(1966). That risk would have justified the police in entering
McArthur's trailer promptly to make a lawful, warrantless search. United States v. Santana, 427 U. S. 38 , 42-43
(1976); Warden, Md. Penitentiary v. Hayden, 387 U. S. 294 , 298-299
(1967). When McArthur stepped 338 outside and left the trailer uninhabited, the risk abated and so
did the reasonableness of entry by the police for as long as he was
outside. This is so because the only justification claimed for
warrantless action here is the immediate risk, and the limit of
reasonable response by the police is set by the scope of the risk.
See Terry v. Ohio, 392 U. S. 1 ,25-26
(1968).

															Since, however, McArthur wished to go back in, why was it
reasonable to keep him out when the police could perfectly well
have let him do as he chose, and then enjoyed the ensuing
opportunity to follow him and make a warrantless search justified
by the renewed danger of destruction? The answer is not that the
law officiously insists on safeguarding a suspect's privacy from
search, in preference to respecting the suspect's liberty to enter
his own dwelling. Instead, the legitimacy of the decision to
impound the dwelling follows from the law's strong preference for
warrants, which underlies the rule that a search with a warrant has
a stronger claim to justification on later, judicial review than a
search without one. See United States v. Ventresca, 380 U. S. 102 ,
106 (1965); see also 5 W. LaFave, Search and Seizure § 11.2(b), p.
38 (3d ed. 1996) ("[M]ost states follow the rule which is utilized
in the federal courts: if the search or seizure was pursuant to a
warrant, the defendant has the burden of proof; but if the police
acted without a warrant the burden of proof is on the
prosecution"). The law can hardly raise incentives to obtain a
warrant without giving the police a fair chance to take their
probable cause to a magistrate and get one.

															JUSTICE STEVENS, dissenting.

															The Illinois General Assembly has decided that the possession of
less than 2.5 grams of marijuana is a class C misdemeanor. See Ill.
Compo Stat., ch. 720, § 550/4(a) (1998). In so classifying the
offense, the legislature made a concerted policy judgment that the
possession of small amounts of 339 marijuana for personal use does not constitute a particularly
significant public policy concern. While it is true that this
offense-like feeding livestock on a public highway or offering a
movie for rent without clearly displaying its rating 1_ may warrant
a jail sentence of up to 30 days, the detection and prosecution of
possessors of small quantities of this substance is by no means a
law enforcement priority in the State of Illinois.2

															Because the governmental interest implicated by the particular
criminal prohibition at issue in this case is so slight, this is a
poor vehicle for probing the boundaries of the government's power
to limit an individual's possessory interest in his or her home
pending the arrival of a search warrant. Cf. Segura v. United States, 468 U. S. 796 (1984)
(seven Justices decline to address this issue because case does not
require its resolution). Given my preference, I would, therefore,
dismiss the writ of certiorari as improvidently granted.

															Compelled by the vote of my colleagues to reach the merits, I
would affirm. As the majority explains, the essential inquiry in
this case involves a balancing of the "privacy-

															1 See Ill. Compo Stat., ch. 605, § 5/9-124.1 (1998) (making
feeding livestock on a public highway a class C misdemeanor); ch.
720, §§ 395/3-395/4 (making it a class C misdemeanor to sell or
rent a video that does not display the official rating of the
motion picture from which it is copied). Other examples of offenses
classified as class C misdemeanors in Illinois include camping on
the side of a public highway, ch. 605, § 5/9-124, interfering with
the "lawful taking of wild animals," ch. 720, § 125/2, and
tattooing the body of a person under 21 years of age, ch. 720, §
5/12-10.

															2 Nor in many other States. Under the laws of many other States,
the maximum penalty McArthur would have faced for possession of 2.3
grams of marijuana would have been less than what he faced in
Illinois. See, e. g., Cal. Health & Safety Code Ann. §
11357(b) (West 1991) ($100 fine); Colo. Rev. Stat. § 18-18-406(1)
(1999) ($100 fine); Minn. Stat. § 152.027(4) (2000) ($200 fine and
drug education); Miss. Code Ann. §41-29-139(c)(2)(A) (Supp. 1999)
($100-$250 fine); Neb. Rev. Stat. §28-416(13) (1995) ($100 fine and
drug education); N. M. Stat. Ann. § 30-31-23(B) (1997) ($50-$100
fine and 15 days in jail); N. Y. Penal Law §221.05 (McKinney 2000)
($100 fine); Ore. Rev. Stat. § 475.992(4)(f) (Supp. 1998) ($100
fine). 340 related and law enforcement-related concerns to determine if the
intrusion was reasonable." Ante, at 331. Under the specific
facts of this case, I believe the majority gets the balance wrong.
Each of the Illinois jurists who participated in the decision of
this case placed a higher value on the sanctity of the ordinary
citizen's home than on the prosecution of this petty offense. They
correctly viewed that interest-whether the home be a humble
cottage, a secondhand trailer, or a stately mansion-as one meriting
the most serious constitutional protection.3 Following their
analysis and the reasoning in our decision in Welsh v. Wisconsin, 466 U. S. 740 (1984) (holding that some offenses
may be so minor as to make it unreasonable for police to undertake
searches that would be constitutionally permissible if graver
offenses were suspected), I would affirm.

															3 Principled respect for the sanctity of the home has long
animated this Court's Fourth Amendment jurisprudence. See, e. g., Wilson v. Layne, 526 U. S. 603 , 610 (1999)
("The Fourth Amendment embodies this centuries-old principle of
respect for the privacy of the home"); Payton v. New
York, 445 U. S.
573 , 601 (1980) (emphasizing "the overriding respect for the
sanctity of the home that has been embedded in our traditions since
the origins of the Republic"); Mincey v. Arizona, 437 U. S. 385 ,
393 (1978) ("[T]he Fourth Amendment reflects the view of those who
wrote the Bill of Rights that the privacy of a person's home and
property may not be totally sacrificed in the name of maximum
simplicity in enforcement of the criminal law").


OCTOBER TERM, 2000

															Syllabus

															KYLLO v. UNITED STATES

															CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE NINTH
CIRCUIT

															No. 99-8508. Argued February 20, 200l-Decided June 11,2001

															Suspicious that marijuana was being grown in petitioner Kyllo's
home in a triplex, agents used a thermal-imaging device to scan the
triplex to determine if the amount of heat emanating from it was
consistent with the high-intensity lamps typically used for indoor
marijuana growth. The scan showed that Kyllo's garage roof and a
side wall were relatively hot compared to the rest of his home and
substantially warmer than the neighboring units. Based in part on
the thermal imaging, a Federal Magistrate Judge issued a warrant to
search Kyllo's home, where the agents found marijuana growing.
After Kyllo was indicted on a federal drug charge, he
unsuccessfully moved to suppress the evidence seized from his home
and then entered a conditional guilty plea. The Ninth Circuit
ultimately affirmed, upholding the thermal imaging on the ground
that Kyllo had shown no subjective expectation of privacy because
he had made no attempt to conceal the heat escaping from his home.
Even if he had, ruled the court, there was no objectively
reasonable expectation of privacy because the thermal imager did
not expose any intimate details of Kyllo's life, only amorphous hot
spots on his home's exterior. Held: Where, as here, the Government uses a device that
is not in general public use, to explore details of a private home
that would previously have been unknowable without physical
intrusion, the surveillance is a Fourth Amendment "search," and is
presumptively unreasonable without a warrant. Pp. 31-41.

															(a) The question whether a warrantless search of a home is
reasonable and hence constitutional must be answered no in most
instances, but the antecedent question whether a Fourth Amendment
"search" has occurred is not so simple. This Court has approved
warrantless visual surveillance of a home, see California v. Ciraolo, 476
U. S. 207 , 213, ruling that visual observation is no "search"
at all, see Dow Chemical Co. v. United States, 476 U. S. 227 ,
234-235, 239. In assessing when a search is not a search, the Court
has adapted a principle first enunciated in Katz v. United States, 389 U. S. 347 , 361: A
"search" does not occur-even when its object is a house explicitly
protected by the Fourth Amendment-unless the individual manifested
a subjective 28 Syllabus

															expectation of privacy in the searched object, and society is
willing to recognize that expectation as reasonable, see, e. g.,
California v. Ciraolo, supra, at 211. Pp. 31-33.

															(b) While it may be difficult to refine the Katz test in
some instances, in the case of the search of a home's interior-the
prototypical and hence most commonly litigated area of protected
privacy-there is a ready criterion, with roots deep in the common
law, of the minimal expectation of privacy that exists, and
that is acknowledged to be reasonable. To withdraw
protection of this minimum expectation would be to permit police
technology to erode the privacy guaranteed by the Fourth Amendment.
Thus, obtaining by sense-enhancing technology any information
regarding the home's interior that could not otherwise have been
obtained without physical "intrusion into a constitutionally
protected area," Silverman v. United States, 365 U. S. 505 , 512,
constitutes a search-at least where (as here) the technology in
question is not in general public use. This assures preservation of
that degree of privacy against government that existed when the
Fourth Amendment was adopted. Pp. 33-35.

															(c) Based on this criterion, the information obtained by the
thermal imager in this case was the product of a search. The Court
rejects the Government's argument that the thermal imaging must be
upheld because it detected only heat radiating from the home's
external surface. Such a mechanical interpretation of the Fourth
Amendment was rejected in Katz, where the eavesdropping
device in question picked up only sound waves that reached the
exterior of the phone booth to which it was attached. Reversing
that approach would leave the homeowner at the mercy of advancing
technology-including imaging technology that could discern all
human activity in the home. Also rejected is the Government's
contention that the thermal imaging was constitutional because it
did not detect "intimate details." Such an approach would be wrong
in principle because, in the sanctity of the home, all details are intimate details. See, e. g., United States v. Karo, 468 U. S. 705; Dow Chemical, supra, at 238,
distinguished. It would also be impractical in application, failing
to provide a workable accommodation between law enforcement needs
and Fourth Amendment interests. See Oliver v. United
States, 466 U. S.
170 , 181. Pp. 35-40.

															(d) Since the imaging in this case was an unlawful search, it
will remain for the District Court to determine whether, without
the evidence it provided, the search warrant was supported by
probable cause-and if not, whether there is any other basis for
supporting admission of that evidence. P. 40. 190 F.3d
1041 , reversed and remanded. 29 SCALIA, J., delivered the opinion of the Court, in which SOUTER,
THOMAS, GINSBURG, and BREYER, JJ., joined. STEVENS, J., filed a
dissenting opinion, in which REHNQUIST, C. J., and O'CONNOR and
KENNEDY, JJ., joined, post, p. 41. Kenneth Lerner, by appointment of the Court, 531 U. S.
955, argued the cause and filed briefs for petitioner.

															Deputy Solicitor General Dreeben argued the cause for the United
States. With him on the brief were former Solicitor General Waxman,
Assistant Attorney General Robinson, Irving L. Gornstein, and
Deborah Watson. *

															JUSTICE SCALIA delivered the opinion of the Court.

															This case presents the question whether the use of a
thermal-imaging device aimed at a private home from a public street
to detect relative amounts of heat within the home constitutes a
"search" within the meaning of the Fourth Amendment.

															I

															In 1991 Agent William Elliott of the United States Department of
the Interior came to suspect that marijuana was being grown in the
home belonging to petitioner Danny Kyllo, part of a triplex on
Rhododendron Drive in Florence, Oregon. Indoor marijuana growth
typically requires highintensity lamps. In order to determine
whether an amount of heat was emanating from petitioner's home
consistent with the use of such lamps, at 3:20 a.m. on January 16,
1992, Agent Elliott and Dan Haas used an Agema Thermovision 210
thermal imager to scan the triplex. Thermal imagers detect infrared
radiation, which virtually all objects emit but which is not
visible to the naked eye. The imager converts radiation into images
based on relative warmth-black

															*Briefs of amici curiae urging reversal were filed for
the Liberty Project by Julie M. Carpenter; and for the
National Association of Criminal Defense Lawyers et al. by James J. Tomkovicz, Lisa B. Kemler, and Steven R.
Shapiro. 30 is cool, white is hot, shades of gray connote relative
differences; in that respect, it operates somewhat like a video
camera showing heat images. The scan of Kyllo's home took only a
few minutes and was performed from the passenger seat of Agent
Elliott's vehicle across the street from the front of the house and
also from the street in back of the house. The scan showed that the
roof over the garage and a side wall of petitioner's home were
relatively hot compared to the rest of the home and substantially
warmer than neighboring homes in the triplex. Agent Elliott
concluded that petitioner was using halide lights to grow marijuana
in his house, which indeed he was. Based on tips from informants,
utility bills, and the thermal imaging, a Federal Magistrate Judge
issued a warrant authorizing a search of petitioner's home, and the
agents found an indoor growing operation involving more than 100
plants. Petitioner was indicted on one count of manufacturing
marijuana, in violation of 21 U. s. C. § 841(a)(1). He
unsuccessfully moved to suppress the evidence seized from his home
and then entered a conditional guilty plea.

															The Court of Appeals for the Ninth Circuit remanded the case for
an evidentiary hearing regarding the intrusiveness of thermal
imaging. On remand the District Court found that the Agema 210 "is
a non-intrusive device which emits no rays or beams and shows a
crude visual image of the heat being radiated from the outside of
the house"; it "did not show any people or activity within the
walls of the structure"; "[t]he device used cannot penetrate walls
or windows to reveal conversations or human activities"; and "[n]o
intimate details of the home were observed." Supp. App. to Pet. for
Cert. 39-40. Based on these findings, the District Court upheld the
validity of the warrant that relied in part upon the thermal
imaging, and reaffirmed its denial of the motion to suppress. A
divided Court of Appeals initially reversed, 140
F.3d 1249 (1998), but that 31 opinion was withdrawn and the panel (after a change in
composition) affirmed, 190 F.3d
1041 (1999), with Judge Noonan dissenting. The court held that
petitioner had shown no subjective expectation of privacy because
he had made no attempt to conceal the heat escaping from his home,
id., at 1046, and even if he had, there was no objectively
reasonable expectation of privacy because the imager "did not
expose any intimate details of Kyllo's life," only "amorphous 'hot
spots' on the roof and exterior wall," id., at 1047. We granted
certiorari. 530 U. S. 1305 (2000).

															II

															The Fourth Amendment provides that "[t]he right of the people to
be secure in their persons, houses, papers, and effects, against
unreasonable searches and seizures, shall not be violated." "At the
very core" of the Fourth Amendment "stands the right of a man to
retreat into his own home and there be free from unreasonable
governmental intrusion." Silverman v. United States, 365 U. S. 505 ,
511 (1961). With few exceptions, the question whether a warrantless
search of a home is reasonable and hence constitutional must be
answered no. See Illinois v. Rodriguez, 497 U. S. 177 , 181
(1990); Payton v. New York, 445 U. S. 573 , 586
(1980).

															On the other hand, the antecedent question whether or not a
Fourth Amendment "search" has occurred is not so simple under our
precedent. The permissibility of ordinary visual surveillance of a
home used to be clear because, well into the 20th century, our
Fourth Amendment jurisprudence was tied to common-law trespass.
See, e. g., Goldman v. United States, 316 U. S. 129 , 134-136
(1942); Olmstead v. United States, 277 U. S. 438 , 464-466
(1928). Cf. Silverman v. United States, supra, at
510-512 (technical trespass not necessary for Fourth Amendment
violation; it suffices if there is "actual intrusion into a
constitutionally protected area"). Visual surveillance was
unquestionably lawful because" 'the 32 eye cannot by the laws of England be guilty of a trespass.'" Boyd v. United States, 116 U. S. 616 , 628 (1886)
(quoting Entick v. Carrington, 19 How. St. Tr. 1029,
95 Eng. Rep. 807 (K. B. 1765)). We have since decoupled violation
of a person's Fourth Amendment rights from trespassory violation of
his property, see Rakas v. III inois, 439 U. S. 128 , 143
(1978), but the lawfulness of warrantless visual surveillance of a
home has still been preserved. As we observed in California v. Ciraolo, 476 U. S. 207 , 213
(1986), "[t]he Fourth Amendment protection of the home has never
been extended to require law enforcement officers to shield their
eyes when passing by a home on public thoroughfares."

															One might think that the new validating rationale would be that
examining the portion of a house that is in plain public view,
while it is a "search" 1 despite the absence of trespass, is not an
"unreasonable" one under the Fourth Amendment. See Minnesota v. Carter, 525
U. S. 83 , 104 (1998) (BREYER, J., concurring in judgment). But
in fact we have held that visual observation is no "search" at
allperhaps in order to preserve somewhat more intact our doctrine
that warrantless searches are presumptively unconstitutional. See Dow Chemical Co. v. United States, 476 U. S. 227,
234-235, 239 (1986). In assessing when a search is not a search, we
have applied somewhat in reverse the principle first enunciated in Katz v. United States, 389 U. S. 347 (1967). Katz involved eavesdropping by means of an electronic
listening device placed on the outside of a telephone booth-a
location not within the catalog ("persons, houses, papers, and
effects") that the Fourth Amendment protects against unreasonable
searches. We held that the

															1 When the Fourth Amendment was adopted, as now, to "search"
meant "[tJo look over or through for the purpose of finding
something; to explore; to examine by inspection; as, to search the house for a book; to search the wood for a
thief." N. Webster, An American Dictionary of the English Language
66 (1828) (reprint 6th ed. 1989). 33 Fourth Amendment nonetheless protected Katz from the warrantless
eavesdropping because he "justifiably relied" upon the privacy of
the telephone booth. Id., at 353. As Justice Harlan's
oft-quoted concurrence described it, a Fourth Amendment search
occurs when the government violates a subjective expectation of
privacy that society recognizes as reasonable. See id., at 361. We
have subsequently applied this principle to hold that a Fourth
Amendment search does not occur-even when the explicitly
protected location of a house is concerned-unless "the
individual manifested a subjective expectation of privacy in the
object of the challenged search," and "society [is] willing to
recognize that expectation as reasonable." Ciraolo, supra, at 211. We have applied this test in holding that it is not a
search for the police to use a pen register at the phone company to
determine what numbers were dialed in a private home, Smith v. Maryland, 442 U. S. 735 , 743744
(1979), and we have applied the test on two different occasions in
holding that aerial surveillance of private homes and surrounding
areas does not constitute a search, Ciraolo, supra; Florida v. Riley, 488
U. S. 445 (1989).

															The present case involves officers on a public street engaged in
more than naked-eye surveillance of a home. We have previously
reserved judgment as to how much technological enhancement of
ordinary perception from such a vantage point, if any, is too much.
While we upheld enhanced aerial photography of an industrial
complex in Dow Chemical, we noted that we found "it
important that this is not an area immediately adjacent to a
private home, where privacy expectations are most heightened," 476
U. S., at 237, n. 4 (emphasis in original).

															III

															It would be foolish to contend that the degree of privacy
secured to citizens by the Fourth Amendment has been 34 entirely unaffected by the advance of technology. For example,
as the cases discussed above make clear, the technology enabling
human flight has exposed to public view (and hence, we have said,
to official observation) uncovered portions of the house and its
curtilage that once were private. See Ciraolo, supra, at
215. The question we confront today is what limits there are upon
this power of technology to shrink the realm of guaranteed
privacy.

															The Katz test-whether the individual has an expectation
of privacy that society is prepared to recognize as reasonable-has
often been criticized as circular, and hence subjective and
unpredictable. See 1 W. LaFave, Search and Seizure § 2.1(d), pp.
393-394 (3d ed. 1996); Posner, The Uncertain Protection of Privacy
by the Supreme Court, 1979 S. Ct. Rev. 173, 188; Carter,
supra, at 97 (SCALIA, J., concurring). But see Rakas,
supra, at 143-144, n.12. While it may be difficult to refine Katz when the search of areas such as telephone booths,
automobiles, or even the curtilage and uncovered portions of
residences is at issue, in the case of the search of the interior
of homes-the prototypical and hence most commonly litigated area of
protected privacythere is a ready criterion, with roots deep in the
common law, of the minimal expectation of privacy that exists, and that is acknowledged to be reasonable. To
withdraw protection of this minimum expectation would be to permit
police technology to erode the privacy guaranteed by the Fourth
Amendment. We think that obtaining by senseenhancing technology any
information regarding the interior of the home that could not
otherwise have been obtained without physical "intrusion into a
constitutionally protected area," Silverman, 365 U. S., at
512, constitutes a searchat least where (as here) the technology in
question is not in general public use. This assures preservation of
that degree of privacy against government that existed when the
Fourth Amendment was adopted. On the basis of this criterion,
the 35 information obtained by the thermal imager in this case was the
product of a search.2

															The Government maintains, however, that the thermal imaging must
be upheld because it detected "only heat radiating from the
external surface of the house," Brief for United States 26. The
dissent makes this its leading point, see post, at 41,
contending that there is a fundamental difference between what it
calls "off-the-wall" observations and "through-the-wall
surveillance." But just as a thermal imager captures only heat
emanating from a house, so also a powerful directional microphone
picks up only sound emanating from a house-and a satellite capable
of scanning from many miles away would pick up only visible light
emanating from a house. We rejected such a mechanical
interpretation of the Fourth Amendment in Katz, where the
eavesdropping device picked up only sound waves that reached the
exterior of the phone booth. Reversing that approach would leave
the homeowner at the mercy of advancing technologyincluding imaging
technology that could discern all human

															2 The dissent's repeated assertion that the thermal imaging did
not obtain information regarding the interior of the home, post, at 43, 44 (opinion of STEVENS, J.), is simply
inaccurate. A thermal imager reveals the relative heat of various
rooms in the home. The dissent may not find that information
particularly private or important, see post, at 43-44, 45,
4950, but there is no basis for saying it is not information
regarding the interior of the home. The dissent's comparison of the
thermal imaging to various circumstances in which outside observers
might be able to perceive, without technology, the heat of the
home-for example, by observing snowmelt on the roof, post, at 43-is quite irrelevant. The fact that equivalent information
could sometimes be obtained by other means does not make lawful the
use of means that violate the Fourth Amendment. The police might,
for example, learn how many people are in a particular house by
setting up year-round surveillance; but that does not make breaking
and entering to find out the same information lawful. In any event,
on the night of January 16, 1992, no outside observer could have
discerned the relative heat of Kyllo's home without thermal
imaging. 36 activity in the home. While the technology used in the present
case was relatively crude, the rule we adopt must take account of
more sophisticated systems that are already in use or in
development.3 The dissent's reliance on the distinction between
"off-the-wall" and "through-the-wall" observation is entirely
incompatible with the dissent's belief, which we discuss below,
that thermal-imaging observations of the intimate details of a home
are impermissible. The most sophisticated thermal-imaging devices
continue to measure heat "off-the-wall" rather than
"through-the-wall"; the dissent's disapproval of those more
sophisticated thermalimaging devices, see post, at 49, is an
acknowledgment that there is no substance to this distinction. As
for the dissent's extraordinary assertion that anything learned
through "an inference" cannot be a search, see post, at 44,
that would validate even the "through-the-wall" technologies that
the dissent purports to disapprove. Surely the dissent does not
believe that the through-the-wall radar or ultrasound technology
produces an 8-by-10 Kodak glossy that needs no analysis (i. e., the making of inferences). And, of course, the novel
proposition that inference insulates a search is blatantly contrary
to United States v. Karo, 468 U. S. 705 (1984),
where the police "inferred" from the activation of a beeper that a
certain can of ether was in the home. The police ac-

															3 The ability to "see" through walls and other opaque barriers
is a clear, and scientifically feasible, goal of law enforcement
research and development. The National Law Enforcement and
Corrections Technology Center, a program within the United States
Department of Justice, features on its Internet Website projects
that include a "RadarBased Through-the-Wall Surveillance System,"
"Handheld Ultrasound Through the Wall Surveillance," and a "Radar
Flashlight" that "will enable law enforcement officers to detect
individuals through interior building walls." www.nlectc.org/techproj/ (visited May 3, 2001). Some devices may emit low levels of
radiation that travel "through-the-wall," but others, such as more
sophisticated thermal-imaging devices, are entirely passive, or
"off-the-wall" as the dissent puts it. 37 tivity was held to be a search, and the search was held
unlawfu1.4

															The Government also contends that the thermal imaging was
constitutional because it did not "detect private activities
occurring in private areas," Brief for United States 22. It points
out that in Dow Chemical we observed that the enhanced
aerial photography did not reveal any "intimate details." 476 U.
S., at 238. Dow Chemical, however, involved enhanced aerial
photography of an industrial complex, which does not share the
Fourth Amendment sanctity of the home. The Fourth Amendment's
protection of the home has never been tied to measurement of the
quality or quantity of information obtained. In Silverman, for example, we made clear that any physical invasion of the
structure of the home, "by even a fraction of an inch," was too
much, 365 U. S., at 512, and there is certainly no exception to the
warrant requirement for the officer who barely cracks open the
front door and sees nothing but the nonintimate rug on the
vestibule floor. In the home, our cases show, all details
are intimate details, because the entire area is held safe from
prying government eyes. Thus, in Karo, supra, the only thing
detected was a can of ether in the

															4 The dissent asserts, post, at 44-45, n. 3, that we have
misunderstood its point, which is not that inference insulates a search, but that inference alone is not a
search. If we misunderstood the point, it was only in a good-faith
effort to render the point germane to the case at hand. The issue
in this case is not the police's allegedly unlawful inferencing,
but their allegedly unlawful thermal-imaging measurement of the
emanations from a house. We say such measurement is a search; the
dissent says it is not, because an inference is not a search. We
took that to mean that, since the technologically enhanced
emanations had to be the basis of inferences before anything inside
the house could be known, the use of the emanations could not be a
search. But the dissent certainly knows better than we what it
intends. And if it means only that an inference is not a search, we
certainly agree. That has no bearing, however, upon whether hi-tech
measurement of emanations from a house is a search. 38 home; and in Arizona v. Hicks, 480 U. S. 321 (1987), the
only thing detected by a physical search that went beyond what
officers lawfully present could observe in "plain view" was the
registration number of a phonograph turntable. These were intimate
details because they were details of the home, just as was the
detail of how warm-or even how relatively warm-Kyllo was heating
his residence.5

															Limiting the prohibition of thermal imaging to "intimate
details" would not only be wrong in principle; it would be
impractical in application, failing to provide "a workable
accommodation between the needs of law enforcement and the
interests protected by the Fourth Amendment," Oliver v. United States, 466 U. S. 170 , 181
(1984). To begin with, there is no necessary connection between the
sophistication of the surveillance equipment and the "intimacy" of
the details that it observes-which means that one cannot say (and
the police cannot be assured) that use of the relatively crude
equipment at issue here will always be lawful. The Agema
Thermovision 210 might disclose, for example, at what hour each
night the lady of the house takes her daily sauna and bath-a detail
that many would consider "intimate"; and a much more sophisticated
system might detect nothing more intimate than the fact that
someone left a closet light on. We could not, in other words,
develop a rule approving only that through-the-wall surveillance
which identifies objects no smaller than 36 by 36 inches, but would
have to develop a jurisprudence specifying which

															5The Government cites our statement in California v. Ciraolo, 476 U. S. 207 (1986), noting apparent agreement
with the State of California that aerial surveillance of a house's
curtilage could become "'invasive'" if "'modern technology'"
revealed "'those intimate associations, objects or activities
otherwise imperceptible to police or fellow citizens.'" Id., at 215, n. 3 (quoting Brief for State of California 14-15). We
think the Court's focus in this secondhand dictum was not upon
intimacy but upon otherwise-imperceptibility, which is precisely
the principle we vindicate today. 39 home activities are "intimate" and which are not. And even when
(if ever) that jurisprudence were fully developed, no police
officer would be able to know in advance whether his
through-the-wall surveillance picks up "intimate" detailsand thus
would be unable to know in advance whether it is
constitutional.

															The dissent's proposed standard-whether the technology offers
the "functional equivalent of actual presence in the area being
searched," post, at 47-would seem quite similar to our own
at first blush. The dissent concludes that Katz was such a
case, but then inexplicably asserts that if the same listening
device only revealed the volume of the conversation, the
surveillance would be permissible, post, at 49-50. Yet if,
without technology, the police could not discern volume without
being actually present in the phone booth, JUSTICE STEVENS should
conclude a search has occurred. Cf. Karo, 468 U. S., at 735
(STEVENS, J., concurring in part and dissenting in part) ("I find
little comfort in the Court's notion that no invasion of privacy
occurs until a listener obtains some significant information by use
of the device .... A bathtub is a less private area when the
plumber is present even if his back is turned"). The same should
hold for the interior heat of the home if only a person present in
the home could discern the heat. Thus the driving force of the
dissent, despite its recitation of the above standard, appears to
be a distinction among different types of information-whether the
"homeowner would even care if anybody noticed," post, at 50.
The dissent offers no practical guidance for the application of
this standard, and for reasons already discussed, we believe there
can be none. The people in their houses, as well as the police,
deserve more precision.6

															6 The dissent argues that we have injected potential uncertainty
into the constitutional analysis by noting that whether or not the
technology is in general public use may be a factor. See post, at 47. That quarrel, 40 We have said that the Fourth Amendment draws "a firm line at the
entrance to the house," Payton, 445 U. S., at 590. That
line, we think, must be not only firm but also brightwhich requires
clear specification of those methods of surveillance that require a
warrant. While it is certainly possible to conclude from the
videotape of the thermal imaging that occurred in this case that no
"significant" compromise of the homeowner's privacy has occurred,
we must take the long view, from the original meaning of the Fourth
Amendment forward. "The Fourth Amendment is to be construed in the light of what
was deemed an unreasonable search and seizure when it was adopted,
and in a manner which will conserve public interests as well as the
interests and rights of individual citizens." Carroll v. United States, 267 U. S. 132, 149 (1925). Where, as here, the Government uses a device that is not in
general public use, to explore details of the home that would
previously have been unknowable without physical intrusion, the
surveillance is a "search" and is presumptively unreasonable
without a warrant.

															Since we hold the Thermovision imaging to have been an unlawful
search, it will remain for the District Court to determine whether,
without the evidence it provided, the search warrant issued in this
case was supported by probable cause-and if not, whether there is
any other basis for supporting admission of the evidence that the
search pursuant to the warrant produced.

															however, is not with us but with this Court's precedent. See Ciraolo, supra, at 215 ("In an age where private and
commercial flight in the public airways is routine, it is
unreasonable for respondent to expect that his marijuana plants
were constitutionally protected from being observed with the naked
eye from an altitude of 1,000 feet"). Given that we can quite
confidently say that thermal imaging is not "routine," we decline
in this case to reexamine that factor. 41 ***

															The judgment of the Court of Appeals is reversed; the case is
remanded for further proceedings consistent with this opinion.

															It is so ordered.

															JUSTICE STEVENS, with whom THE CHIEF JUSTICE, JusTICE O'CONNOR,
and JUSTICE KENNEDY join, dissenting.

															There is, in my judgment, a distinction of constitutional
magnitude between "through-the-wall surveillance" that gives the
observer or listener direct access to information in a private
area, on the one hand, and the thought processes used to draw
inferences from information in the public domain, on the other
hand. The Court has crafted a rule that purports to deal with
direct observations of the inside of the home, but the case before
us merely involves indirect deductions from "off-the-wall"
surveillance, that is, observations of the exterior of the home.
Those observations were made with a fairly primitive thermal imager
that gathered data exposed on the outside of petitioner's home but
did not invade any constitutionally protected interest in privacy.l
Moreover, I believe that the supposedly "bright-line" rule the
Court has created in response to its concerns about future
technological developments is unnecessary, unwise, and inconsistent
with the Fourth Amendment.

															I

															There is no need for the Court to craft a new rule to decide
this case, as it is controlled by established principles from

															1 After an evidentiary hearing, the District Court found:

															"[T]he use of the thermal imaging device here was not an
intrusion into Kyllo's home. No intimate details of the home were
observed, and there was no intrusion upon the privacy of the
individuals within the home. The device used cannot penetrate walls
or windows to reveal conversations or human activities. The device
recorded only the heat being emitted from the home." Supp. App. to
Pet. for Cert. 40. 42 our Fourth Amendment jurisprudence. One of those core
principles, of course, is that "searches and seizures inside a
home without a warrant are presumptively unreasonable." Payton v. New York, 445 U. S. 573 , 586 (1980)
(emphasis added). But it is equally well settled that searches and
seizures of property in plain view are presumptively reasonable.
See id., at 586-587.2 Whether that property is residential or
commercial, the basic principle is the same: "'What a person
knowingly exposes to the public, even in his own home or office, is
not a subject of Fourth Amendment protection.'" California v. Ciraolo, 476 U. S. 207 , 213 (1986)
(quoting Katz v. United States, 389 U. S. 347 , 351
(1967)); see Florida v. Riley, 488 U. S. 445 , 449-450 (1989); California v. Greenwood, 486 U. S. 35 , 40-41
(1988); Dow Chemical Co. v. United States, 476 U. S. 227 , 235-236 (1986); Air Pollution Variance Bd. of Colo. v. Western
Alfalfa Corp., 416 U. S. 861 , 865
(1974). That is the principle implicated here.

															While the Court "take[s] the long view" and decides this case
based largely on the potential of yet-to-be-developed technology
that might allow "through-the-wall surveillance," ante, at
38-40; see ante, at 36, n. 3, this case involves nothing
more than off-the-wall surveillance by law enforcement officers to
gather information exposed to the general public from the outside
of petitioner's home. All that the infrared camera did in this case
was passively measure heat emitted

															2 Thus, for example, we have found consistent with the Fourth
Amendment, even absent a warrant, the search and seizure of garbage
left for collection outside the curtilage of a home, California v. Greenwood, 486 U. S. 35 (1988); the
aerial surveillance of a fenced-in backyard from an altitude of
1,000 feet, California v. Ciraolo, 476 U. S. 207 (1986); the
aerial observation of a partially exposed interior of a residential
greenhouse from 400 feet above, Florida v. Riley, 488 U. S. 445 (1989); the aerial photography of an industrial complex from
several thousand feet above, Dow Chemical Co. v. United
States, 476 U. S.
227 (1986); and the observation of smoke emanating from chimney
stacks, Air Pollution Variance Bd. of Colo. v. Western
Alfalfa Corp., 416 U. S. 861 (1974). 43 from the exterior surfaces of petitioner's home; all that those
measurements showed were relative differences in emission levels,
vaguely indicating that some areas of the roof and outside walls
were warmer than others. As still images from the infrared scans
show, see Appendix, infra, no details regarding the interior
of petitioner's home were revealed. Unlike an x-ray scan, or other
possible "throughthe-wall" techniques, the detection of infrared
radiation emanating from the home did not accomplish "an
unauthorized physical penetration into the premises," Silverman v. United States, 365 U. S. 505 , 509
(1961), nor did it "obtain information that it could not have
obtained by observation from outside the curtilage of the house," United States v. Karo, 468 U. S. 705 , 715
(1984).

															Indeed, the ordinary use of the senses might enable a neighbor
or passerby to notice the heat emanating from a building,
particularly if it is vented, as was the case here. Additionally,
any member of the public might notice that one part of a house is
warmer than another part or a nearby building if, for example,
rainwater evaporates or snow melts at different rates across its
surfaces. Such use of the senses would not convert into an
unreasonable search if, instead, an adjoining neighbor allowed an
officer onto her property to verify her perceptions with a
sensitive thermometer. Nor, in my view, does such observation
become an unreasonable search if made from a distance with the aid
of a device that merely discloses that the exterior of one house,
or one area of the house, is much warmer than another. Nothing more
occurred in this case.

															Thus, the notion that heat emissions from the outside of a
dwelling are a private matter implicating the protections of the
Fourth Amendment (the text of which guarantees the right of people
"to be secure in their ... houses" against unreasonable
searches and seizures (emphasis added)) is not only unprecedented
but also quite difficult to take seriously. Heat waves, like aromas
that are generated in a kitchen, or 44 in a laboratory or opium den, enter the public domain if and
when they leave a building. A subjective expectation that they
would remain private is not only implausible but also surely not
"one that society is prepared to recognize as 'reasonable.'" Katz, 389 U. S., at 361 (Harlan, J., concurring).

															To be sure, the homeowner has a reasonable expectation of
privacy concerning what takes place within the home, and the Fourth
Amendment's protection against physical invasions of the home
should apply to their functional equivalent. But the equipment in
this case did not penetrate the walls of petitioner's home, and
while it did pick up "details of the home" that were exposed to the
public, ante, at 38, it did not obtain "any information
regarding the interior of the home," ante, at 34
(emphasis added). In the Court's own words, based on what the
thermal imager "showed" regarding the outside of petitioner's home,
the officers "concluded" that petitioner was engaging in illegal
activity inside the home. Ante, at 30. It would be quite
absurd to characterize their thought processes as "searches,"
regardless of whether they inferred (rightly) that petitioner was
growing marijuana in his house, or (wrongly) that "the lady of the
house [was taking] her daily sauna and bath." Ante, at 38.
In either case, the only conclusions the officers reached
concerning the interior of the home were at least as indirect as
those that might have been inferred from the contents of discarded
garbage, see California v. Greenwood, 486 U. S. 35 (1988), or
pen register data, see Smith v. Maryland, 442 U. S. 735 (1979), or,
as in this case, subpoenaed utility records, see 190 F.3d
1041 , 1043 (CA9 1999). For the first time in its history, the
Court assumes that an inference can amount to a Fourth Amendment
violation. See ante, at 36-37.3

															3 Although the Court credits us with the "novel proposition that
inference insulates a search," ante, at 36, our point simply
is that an inference cannot be a search, contrary to the
Court's reasoning. See supra this page. Thus, the Court's
use of United States v. Karo, 468 U. S. 705 45 Notwithstanding the implications of today's decision, there is a
strong public interest in avoiding constitutional litigation over
the monitoring of emissions from homes, and over the inferences
drawn from such monitoring. Just as "the police cannot reasonably
be expected to avert their eyes from evidence of criminal activity
that could have been observed by any member of the public," Greenwood, 486 U. S., at 41, so too public officials should
not have to avert their senses or their equipment from detecting
emissions in the public domain such as excessive heat, traces of
smoke, suspicious odors, odorless gases, airborne particulates, or
radioactive emissions, any of which could identify hazards to the
community. In my judgment, monitoring such emissions with
"sense-enhancing technology," ante, at 34, and drawing
useful conclusions from such monitoring, is an entirely reasonable
public service.

															On the other hand, the countervailing privacy interest is at
best trivial. After all, homes generally are insulated to keep heat
in, rather than to prevent the detection of heat going out, and it
does not seem to me that society will suffer from a rule requiring
the rare homeowner who both intends to engage in uncommon
activities that produce extraordinary amounts of heat, and wishes
to conceal that production from outsiders, to make sure that the
surrounding area is well insulated. Cf. United States v. Jacobsen, 466
U. S. 109 , 122 (1984) ("The concept of an interest in privacy
that society is prepared to recognize as reasonable is, by its very
nature, critically different from the mere expectation, however
well

															(1984), to refute a point we do not make underscores the fact
that the Court has no real answer (either in logic or in law) to
the point we do make. Of course, Karo itself does not
provide any support for the Court's view that inferences can amount
to unconstitutional searches. The illegality in that case was "the
monitoring of a beeper in a private residence" to obtain
information that "could not have [been] obtained by observation
from outside," id., at 714-715, rather than any thought processes
that flowed from such monitoring. 46 justified, that certain facts will not come to the attention of
the authorities"). The interest in concealing the heat escaping
from one's house pales in significance to "the chief evil against
which the wording of the Fourth Amendment is directed," the
"physical entry of the home," United States v. United
States Dist. Court for Eastern Dist. of Mich., 407 U. S. 297,
313 (1972), and it is hard to believe that it is an interest the
Framers sought to protect in our Constitution.

															Since what was involved in this case was nothing more than
drawing inferences from off-the-wall surveillance, rather than any
"through-the-wall" surveillance, the officers' conduct did not
amount to a search and was perfectly reasonable.4

															II

															Instead of trying to answer the question whether the use of the
thermal imager in this case was even arguably unreasonable, the
Court has fashioned a rule that is intended to provide essential
guidance for the day when "more sophisticated systems" gain the
"ability to 'see' through walls and other opaque barriers." Ante, at 36, and n. 3. The newly minted rule encompasses
"obtaining [1] by senseenhancing technology [2] any information
regarding the interior of the home [3] that could not otherwise
have been obtained without physical intrusion into a
constitutionally protected area ... [4] at least where (as here)
the technology in question is not in general public use." Ante, at 34 (internal quotation marks omitted). In my
judgment, the

															4 This view comports with that of all the Courts of Appeals that
have resolved the issue. See 190 F.3d
1041 (CA9 1999); United States v. Robinson, 62 F.3d
1325 (CAll 1995) (upholding warrantless use of thermal imager); United States v. Myers, 46 F.3d
668 (CA7 1995) (same); United States v. Ishmael, 48 F.3d
850 (CA5 1995) (same); United States v. Pinson, 24 F.3d
1056 (CA8 1994) (same). But see United States v. Cusumano, 67 F.3d
1497 (CAW 1995) (warrantless use of thermal imager violated
Fourth Amendment), vacated and decided on other grounds, 83 F.3d
1247 (CAW 1996) (en bane). 47 Court's new rule is at once too broad and too narrow, and is not
justified by the Court's explanation for its adoption. As I have
suggested, I would not erect a constitutional impediment to the use
of sense-enhancing technology unless it provides its user with the
functional equivalent of actual presence in the area being
searched.

															Despite the Court's attempt to draw a line that is "not only
firm but also bright," ante, at 40, the contours of its new
rule are uncertain because its protection apparently dissipates as
soon as the relevant technology is "in general public use," ante, at 34. Yet how much use is general public use is not
even hinted at by the Court's opinion, which makes the somewhat
doubtful assumption that the thermal imager used in this case does
not satisfy that criterion.5 In any event, putting aside its lack
of clarity, this criterion is somewhat perverse because it seems
likely that the threat to privacy will grow, rather than recede, as
the use of intrusive equipment becomes more readily available.

															It is clear, however, that the category of "sense-enhancing
technology" covered by the new rule, ibid., is far too
broad. It would, for example, embrace potential mechanical
substitutes for dogs trained to react when they sniff narcotics.
But in United States v. Place, 462 U. S. 696 , 707
(1983), we held that a dog sniff that "discloses only the presence
or absence of narcotics" does "not constitute a 'search' within the
meaning of the Fourth Amendment," and it must follow that
sense-enhancing equipment that identifies nothing but illegal

															5 The record describes a device that numbers close to a thousand
manufactured units; that has a predecessor numbering in the
neighborhood of 4,000 to 5,000 units; that competes with a similar
product numbering from 5,000 to 6,000 units; and that is "readily
available to the public" for commercial, personal, or law
enforcement purposes, and is just an 800number away from being
rented from "half a dozen national companies" by anyone who wants
one. App. 18. Since, by virtue of the Court's new rule, the issue
is one of first impression, perhaps it should order an evidentiary
hearing to determine whether these facts suffice to establish
"general public use." 48 activity is not a search either. Nevertheless, the use of such a
device would be unconstitutional under the Court's rule, as would
the use of other new devices that might detect the odor of deadly
bacteria or chemicals for making a new type of high explosive, even
if the devices (like the dog sniffs) are "so limited both in the
manner in which" they obtain information and "in the content of the
information" they reveal. Ibid. If nothing more than that
sort of information could be obtained by using the devices in a
public place to monitor emissions from a house, then their use
would be no more objectionable than the use of the thermal imager
in this case.

															The application of the Court's new rule to "any information
regarding the interior of the home," ante, at 34, is also
unnecessarily broad. If it takes sensitive equipment to detect an
odor that identifies criminal conduct and nothing else, the fact
that the odor emanates from the interior of a home should not
provide it with constitutional protection. See supra, at 47
and this page. The criterion, moreover, is too sweeping in that
information "regarding" the interior of a home apparently is not
just information obtained through its walls, but also information
concerning the outside of the building that could lead to (however
many) inferences "regarding" what might be inside. Under that
expansive view, I suppose, an officer using an infrared camera to
observe a man silently entering the side door of a house at night
carrying a pizza might conclude that its interior is now occupied
by someone who likes pizza, and by doing so the officer would be
guilty of conducting an unconstitutional "search" of the home.

															Because the new rule applies to information regarding the
"interior" of the home, it is too narrow as well as too broad.
Clearly, a rule that is designed to protect individuals from the
overly intrusive use of sense-enhancing equipment should not be
limited to a home. If such equipment 49 did provide its user with the functional equivalent of access to
a private place-such as, for example, the telephone booth involved
in Katz, or an office building-then the rule should apply to
such an area as well as to a home. See Katz, 389 U. S., at
351 ("[T]he Fourth Amendment protects people, not places").

															The final requirement of the Court's new rule, that the
information "could not otherwise have been obtained without
physical intrusion into a constitutionally protected area," ante, at 34 (internal quotation marks omitted), also extends
too far as the Court applies it. As noted, the Court effectively
treats the mental process of analyzing data obtained from external
sources as the equivalent of a physical intrusion into the home.
See supra, at 44. As I have explained, however, the process
of drawing inferences from data in the public domain should not be
characterized as a search.

															The two reasons advanced by the Court as justifications for the
adoption of its new rule are both unpersuasive. First, the Court
suggests that its rule is compelled by our holding in Katz, because in that case, as in this, the surveillance consisted of
nothing more than the monitoring of waves emanating from a private
area into the public domain. See ante, at 35. Yet there are
critical differences between the cases. In Katz, the
electronic listening device attached to the outside of the phone
booth allowed the officers to pick up the content of the
conversation inside the booth, making them the functional
equivalent of intruders because they gathered information that was
otherwise available only to someone inside the private area; it
would be as if, in this case, the thermal imager presented a view
of the heat-generating activity inside petitioner's home. By
contrast, the thermal imager here disclosed only the relative
amounts of heat radiating from the house; it would be as if, in Katz, the listening device disclosed only the rela- 50 tive volume of sound leaving the booth, which presumably was
discernible in the public domain.6 Surely, there is a significant
difference between the general and well-settled expectation that
strangers will not have direct access to the contents of private
communications, on the one hand, and the rather theoretical
expectation that an occasional homeowner would even care if anybody
noticed the relative amounts of heat emanating from the walls of
his house, on the other. It is pure hyperbole for the Court to
suggest that refusing to extend the holding of Katz to this
case would leave the homeowner at the mercy of "technology that
could discern all human activity in the home." Ante, at
35-36.

															Second, the Court argues that the permissibility of
"through-the-wall surveillance" cannot depend on a distinction
between observing "intimate details" such as "the lady of the house
[taking] her daily sauna and bath," and noticing only "the
nonintimate rug on the vestibule floor" or "objects no smaller than
36 by 36 inches." Ante, at 37, 3839. This entire argument
assumes, of course, that the thermal imager in this case could or
did perform "through-thewall surveillance" that could identify any
detail "that would previously have been unknowable without physical
intrusion." Ante, at 39-40. In fact, the device could not,
see n. 1, supra, and did not, see Appendix, infra, enable its user to identify either the lady of the house, the rug
on the vestibule floor, or anything else inside the house, whether
smaller or larger than 36 by 36 inches. Indeed, the vague thermal
images of petitioner's home that are reproduced in the Appendix
were submitted by him to the District Court as part of an expert
report raising the question whether the device could even take
"accurate, consistent infrared images" of the

															6 The use of the latter device would be constitutional given
Smith v. Maryland, 442 U. S. 735 , 741
(1979), which upheld the use of pen registers to record numbers
dialed on a phone because, unlike "the listening device employed in Katz ... pen registers do not acquire the contents of
communications." 51 outside of his house. Defendant's Exh. 107, p. 4. But
even if the device could reliably show extraordinary differences in
the amounts of heat leaving his home, drawing the inference that
there was something suspicious occurring inside the residence-a
conclusion that officers far less gifted than Sherlock Holmes would
readily draw-does not qualify as "through-the-wall surveillance,"
much less a Fourth Amendment violation.

															III

															Although the Court is properly and commendably concerned about
the threats to privacy that may flow from advances in the
technology available to the law enforcement profession, it has
unfortunately failed to heed the tried and true counsel of judicial
restraint. Instead of concentrating on the rather mundane issue
that is actually presented by the case before it, the Court has
endeavored to craft an all-encompassing rule for the future. It
would be far wiser to give legislators an unimpeded opportunity to
grapple with these emerging issues rather than to shackle them with
prematurely devised constitutional constraints.

															I respectfully dissent.

															[Appendix to opinion of STEVENS, J., follows this page.] 52 Appendix to opinion of STEVENS, J.

															APPENDIX TO OPINION OF STEVENS, J. (Images and text reproduced
from defendant's exhibit 107) Top left: Infrared image of a video
frame from the videotape submitted as evidence in this case. The
thermogram indicates the suspect house as it appeared with the Gain
and contrast in its default setting. Only the outline of the house
is visible. The camera used was the Thermovision 210. Top Right:
Infrared image of a subsequent videoframe taken from the videotape.
The gain and contrast settings have been increased in order to make
the walls and roof of the structure appear hotter than what it
actually is. Bottom Left: Infrared image of the opposite side of the suspects
house. The thermogram is also taken from the same videotape. The
camera settings are in the default mode and the outline of the
house is barely visible. Only the hot electrical transformer and
the street light are identifiable.

															Bottom Right: The same image, but with the gain and contrast
increased. This change in camera settings cause any object to
appear hotter than what it actually is. The arrow indicates the
overloading of an area immediately around a hot object in this case
the electrical transformer and the streetlight. This overloading of
the image is an inherent design flaw in the camera itself.