The authority to do this appears to be based around a blend of legal decisions. The Supreme Court has ruled that police can search your phone if they have a warrant, and that they can order you to produce fingerprints without a judge's approval. However, it's not certain that you can combine the two. 
 
 As the LA Times explains, there's a dispute as to whether or not using your fingerprint to unlock your phone is a violation of the Constitution's 5th Amendment, which protects against self-incrimination. While a fingerprint isn't the same as testifying, unlocking your phone could be treated that way. Even with precedent from a 2014 Virginia case (which determined that fingerprints are okay, but passcodes aren't) working in the feds' favor, there's no guarantee that police can order fingerprint access going forward. 

 A Southern California woman was recently ordered to provide her fingerprint to unlock a seized iPhone, according to a report by the Los Angeles Times. 
 
 The case highlights the ongoing balancing act between security and convenience and how the law treats something you know (a passcode) as being quite different than something you are (a biometric). Under the Constitution, criminal defendants have the right not to testify against themselves—and providing a passcode could be considered testimonial. However, being compelled to give up something physiological or biometric (such as blood, DNA sample, fingerprint or otherwise), is not. 
 
 As the Times reports, Paytsar Bkhchadzhyan was ordered by a federal judge to provide her fingerprint on February 25, and the warrant was executed and unsealed on March 15. 
 
 "Why authorities wanted Bkhchadzhyan to unlock the phone is unclear," the Times noted. "The phone was seized from a Glendale residence linked to Sevak Mesrobian, who according to a probation report was Bkhchadzhyan's boyfriend and a member of the Armenian Power gang with the moniker of ‘40.’" 
 
 iPhones equipped with such a scanner, if that feature is enabled, can only can be unlocked via fingerprint if the phone hasn't been unlocked within 48 hours. If the phone is rebooted or has been sitting for longer than 48 hours, the phone's passcode is required. 
 
 A search of federal court records of both Bkhchadzhyan and Mesrobian came up empty, which suggests that any charges remain sealed or have not yet been filed. 
 
 Cases that have demanded that someone unlock his or her smartphone with their own fingerprint remain relatively rare. In 2014, a Virginia Circuit Court judge found that a person does not need to provide a passcode to unlock their phone for the police, and it also ruled that demanding a suspect to provide a fingerprint to unlock a phone would be constitutional. 
 
 Since Apple introduced Touch ID in 2013, some privacy law experts have warned of relying too much on the fingerprint system. That same year, Marcia Hoffman, a well-known Silicon Valley lawyer, concluded in a Wired op-ed that defendants may be subject to a weakened Fifth Amendment protection against self-incrimination: 
 
 But if we move toward authentication systems based solely on physical tokens or biometrics—things we have or things we are, rather than things we remember—the government could demand that we produce them without implicating anything we know. Which would make it less likely that a valid privilege against self-incrimination would apply. 
 
 A wake-up call 
 
 That logic seems to continue to hold, at least for some of Hoffman’s colleagues. 
 
 "This is why I tell my criminal procedure students that they have more protections if they use a passcode rather than fingerprint to guard entry to their phones," Mary Fan, a law professor at the University of Washington, told Ars by e-mail. "While I don’t conduct crimes on my cell phone, I still decline to use my fingerprint out of an abundance of caution!" 
 
 Riana Pfefferkorn, a cryptography fellow at the Stanford Center for Internet and Society, said that she's not sure there would be a good legal defense to a judicial order such as this one. 
 
 "I don't find this warrant legally problematic under the Fifth Amendment, but it does serve as a wake-up call to folks who may not have been aware of the important legal consequences that hang on which option they pick to protect their phones," she e-mailed. "To be sure, it's troubling to think that the police could end up using against you a choice you made for the sake of convenience and to make it harder for someone to snoop into your phone without your knowledge. But I don't think it runs counter to the Fifth Amendment." 
 
 However, Pfefferkorn added that while she doesn’t currently own a smartphone with Touch ID, she didn’t enable it on her previous phone "for precisely this reason: the legal protection against being compelled to unlock your phone is lesser with fingerprint-unlocking than with entering a passphrase. (Not that I expect to get arrested!)" 
 
 In 2013, Hoffman noted that there is a simple solution to avoid this entire problem: use biometrics in conjunction with passcodes.
– Apple's fight with the feds over unlocking the San Bernardino shooter's phone has dominated the headlines, but a judge demanded a woman's fingerprint be used to unlock her iPhone—a first in a federal court case, reports the Los Angeles Times. Paytsar Bkhchadzhyan's phone was seized from a home in Glendale, Calif., associated with her boyfriend, an alleged Armenian gang member. Less than an hour after Bkhchadzhyan's arrest, a judge ordered the 29-year-old to unlock her iPhone through Apple's Touch ID. She later pleaded no contest to a felony count of identity theft, but the law is murky here: Police can get a warrant to search a phone and can take fingerprints without court approval. But whether they can demand fingerprints to unlock a phone is unclear, per Engadget. An expert says Bkhchadzhyan's phone may have contained incriminating information, meaning the court order violated her Fifth Amendment right in essentially forcing her to testify. "It's the same as if she went home and pulled out paper documents," she says. According to a 2014 court ruling, however, fingerprints are considered "real or physical evidence," the extraction of which doesn't violate the right against self-incrimination. Pass codes, on the other hand, are a form of knowledge and are generally protected. "This is why I tell my criminal procedure students that they have more protections if they use a pass code rather than fingerprint to guard entry to their phones," a law professor tells Ars Technica. "While I don't conduct crimes on my cellphone, I still decline to use my fingerprint out of an abundance of caution."