In a far-reaching ruling in June (Riley v. California), the court unanimously decided that police must obtain a warrant to search the contents of a cell phone seized from someone who is under arrest—except in cases of emergency.

The decision stems from a case in which a motorist was stopped for a routine traffic violation and arrested on weapons charges. Upon arrest the police accessed the driver’s cell phone multiple times without securing a search warrant. The court denied the driver’s motion to suppress the cell phone evidence, and he was subsequently convicted in connection with a shooting, based partially on that evidence.

The Supreme Court reversed the decision of the California Court of Appeal and sent the case back for further proceedings. Summing up the court’s opinion, Chief Justice John Roberts said:

“Modern cell phones are not just another technological convenience. With all they contain and all they may reveal, they hold for many Americans ‘the privacies of life’… The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the Founders fought. Our answer to the question of what police must do before searching a cell phone seized incident to an arrest is accordingly simple—get a warrant.”

The Riley decision is notable because it recognizes that privacy concerns have heightened in the digital age. The chief justice acknowledged this when he wrote that “more substantial privacy interests are at stake when digital data is involved.” He also pointed out that a cell phone collects “many distinct types of information that reveal much more in combination than any isolated record.”

Contrast this with a 2011 California Supreme Court ruling (The People v. Gregory Diaz) that Fourth Amendment protections do not apply to cell phones and the data stored on those phones. In this case, the court found that cell phones are essentially a part of a person’s clothing. The U.S. Supreme Court had previously ruled in favor of warrantless searches of items immediately associated with an arrested person, such as clothing or cigarette packs.

The Riley decision brings the Fourth Amendment into the digital age. It also represents a boost for motorist’s rights, since so many privacy intrusions begin with a simple traffic stop.

But Riley is not a panacea; motorists still face an intimidating gauntlet of privacy challenges. For example, the U.S. Supreme Court ruled (Maryland v. King) in 2013 that police do not need a warrant to take DNA samples from people arrested for serious crimes.

John Whitehead, founder and president of the Rutherford Institute, provided a stark and alarming assessment of King: “Any American who thinks they’re safe from the threat of DNA sampling, blood draws, and roadside strip … searches simply because they’ve ‘done nothing wrong,’ needs to wake up to the new reality in which we’re now living.” (See his full commentary here.) Note the reference to roadside searches.

Whitehead called out the potential impact on motorists again in a radio interview, in which he predicted that people will be subjected to DNA sampling in their vehicles. It’s already happened. In 2008, Florida police, looking for a serial killer, made headlines after taking DNA from “persons of interest” during traffic stops. And don’t forget NHTSA’s ongoing, “voluntary” roadside campaign to collect saliva and blood from as many motorists as possible.

In addition, many law enforcement agencies use cell-phone snooping devices called stingrays, which mimic cell phone towers and capture calling data. Due to strict non-disclosure agreements with the device’s manufacturer, some agencies choose not to reveal their use of stingray technology, not even before a judge to secure a warrant.

According to USA Today, dozens of local and state police forces use stingrays to sweep up cell-phone data, such as caller identity and location information, call and text logs, and other data about users’ communications and movements. Thousands of cell users can be monitored simultaneously, whether they’re a target of a criminal investigation or not. Yet, only 11 states have laws requiring police to get a warrant before using the technology, while 10 others are considering such measures.

Clearly we have a long way to go to ensure motorists receive the privacy protections guaranteed them by the Fourth Amendment. This most recent U.S. Supreme Court decision represents a strong starting point for achieving that goal in the digital era.