In a consolidated decision in Riley v. California and United States v. Wurie, the Court held that a warrantless search of a suspect's cellphone data incident to arrest is unconstitutional. As the opinion by Chief Judge Roberts succinctly put it in closing: "Our answer to the question of what police must do before searching a cell phone seized incident to an arrest is [] simple— get a warrant."

The ruling recognizes the weighty privacy interests implicated by the vast storage capacity of modern cell phones, and the sweeping window into their owners' lives offered by the data they contain. Or, as the Court put it: "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 ruling benefits not only individuals' interests in privacy, but also shores up protections for news organizations whose members use modern technology to record, document, and report events. Given the many ways that journalists and others use cell phone technology, the case goes to the heart of the concerns that led the Constitution's Framers to adopt not only the Fourth Amendment, but also protections for freedom of expression and against self-incrimination.

In Riley, police searched the contents of the defendant's smartphone without a warrant both during and following his arrest, including contact listings and videos. Both the trial court and California Court of Appeal rejected Riley's contention that crucial evidence found during the searches violated the Fourth Amendment. In Wurie, police took possession of the defendant's "flip-phone" after his arrest and accessed its call logs and wallpaper without a warrant. The U.S. Court of Appeals for the 1st vacated Wurie's conviction, stating that the warrantless inspection, which led investigators to incriminating evidence against Wurie, was improper.

Chief Justice Roberts' opinion repeatedly highlighted the fact that many of the Court's prior decisions permitting searches of physical objects incident to arrest hold little logic in the digital age. For example, the Court held that the original justifications for the doctrine – potential harm to officers and destruction of evidence – have "no comparable risks when the search is of digital data." The Court recognized that "[o]nce an officer has secured a phone and eliminated any potential physical threats, . . . data on the phone can endanger no one." It thus held that "search of the information on a cell phone bears little resemblance to the type of brief physical search" considered in previous cases involving, for example, a container in a coat pocket that contained contraband. "Modern cellphones . . . implicate privacy concerns far beyond those implicated by the search of a cigarette pack, a wallet, or a purse," given their data capacity and multifaceted functions.

Chief Justice Roberts wrote that comparing physical items to a cell phone "is like saying a ride on horseback is materially indistinguishable from a flight to the moon. Both are ways of getting from point A to point B, but little else justified lumping them together."

The Court's opinion prominently underscored how cellphones are pervasive in the daily lives of most Americans, noting "the proverbial visitor from Mars might conclude they were an important feature of human anatomy." It observed that modern phones are mini-computers that perform multiple functions and hold immense amount of personal data, and were themselves inconceivable when the Court had originally permitted police to search individuals incident to arrest. Indeed, impositions on a person's privacy through a physical search were relatively narrow before the digital era; however, "the possible intrusion on privacy is not physically limited in the same way when it comes to cell phones." The Court noted that the 1926 observation by noted jurist Learned Hand, "that it is a totally different thing to search a man's pockets and use against him what they contain, from ransacking his house for everything which may incriminate him" is simply "no longer true" if "his pockets contain a cell phone."

Crucially, the Court recognized, searching a cell phone can potentially expose more information to the government than a search of an individual's house, given the amount of data typical phones can store. The fact "that technology now allows an individual to carry such information in his hand does not make the information any less worthy of . . . protection."

The Court acknowledged that its decision will "have an impact on the ability of law enforcement to combat crime." However, it also recognized that "Privacy comes at a cost," and that the warrant requirement is "an important working part of our machinery of government" that must be respected.  And as the Court noted, it expects "the gulf between physical practicability and digital capacity [to] only continue to widen in the future."

The effects of the Riley decision could well be felt beyond traditional law enforcement activities, and may add a new dimension to the ongoing debate over how much governments should be able to intrude into individuals' lives via their own electronic devices. For instance, news organizations and citizen reporters use new communications technologies, including smart phones, as an integral part of their journalistic endeavors. Coverage of breaking news frequently involves contact with police, and journalists have been threatened, arrested, and sometimes charged for doing nothing more than engaging in newsgathering activities. The same has happened to private individuals who use cell phones to record and document newsworthy events, as advanced technology has made citizen reporting more ubiquitous.

These new technologies have greatly expanded the ability to gather and report news, but the same capabilities that make them a boon to journalists create a grave threat if they are subject to unrestricted warrantless searches incident to arrest. Unfortunately, the threat is not just hypothetical, and the enhanced newsgathering capacity may have made reporters more frequent targets of police action. There has been an epidemic of arrests for nothing more than the journalistic enterprise of photographing public events.

If Riley had been decided differently, each such arrest would entitle the police to search the photographs, videos, and notes of the reporters arrested, and reveal electronic communications with sources as well as the reporters' contacts. Now, the Court has given protection to the general public, reporters included, from that kind of invasive search.