Police need a warrant to search the cell phone of a person who has been arrested, absent special circumstances, a unanimous Supreme Court ruled Wednesday.

“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,’” Chief Justice John Roberts wrote. “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.” Close video SCOTUS: Cell phone searches require warrant NBC’s Pete Williams reports on Wednesday’s Supreme Court ruling that requires police to obtain a warrant to search the cell phone of a person who has been arrested. share tweet email Embed

The high court took two cases involving cell phone searches, one involving a smartphone and the other involving a relatively basic flip phone. In both cases, police used information on each phone to connect the plaintiffs to crimes. San Diego Police used pictures in David Leon Riley’s smartphone, and the guns they found in his trunk after pulling him over for a traffic violation, to tie him to a local faction of the Bloods street gang and an earlier shooting. In Boston, Brima Wurie was arrested on suspicion of being involved in selling drugs and a picture linked to a phone call on his flip phone to a stash of crack cocaine.

The decision will likely have long-lasting implications for digital privacy, far beyond the immediate concern surrounding how and when police can search a mobile device. Police are typically allowed to search an individual after an arrest, but Roberts wrote that the amount of personal information contained on a cell phone made such a search different from the usual objects authorities might find when asking someone to empty their pockets.

“A cell phone search would typically expose to the government far more than the most exhaustive search of a house,” he wrote. “A phone not only contains in digital form many sensitive records previously found in the home; it also contains a broad array of private information never found in a home in any form—unless the phone is.”

The court held that the “exigent circumstances” exception to the warrant requirement also applied to cell phones – that is, imminent danger to life or the possibility that evidence would be destroyed might justify searching a phone without a warrant. Justice Samuel Alito, in a concurrence, opened the door to further exceptions. Alito wrote that he would “reconsider the question presented here if either Congress or state legislatures, after assessing the legitimate needs of law enforcement and the privacy interests of cell phone owners, enact legislation that draws reasonable distinctions based on categories of information or perhaps other variables.”

Civil libertarian groups argued that advances in technology mean that the right of individuals to be “secure in their persons, houses, papers or effects” as guaranteed by the Fourth Amendment to the Constitution mean that police should seek warrants before rifling through suspects’ mobile devices. The government countered that those same technological advancements aid criminals, and that remote wiping and encryption could be used to destroy or conceal evidence of serious crimes. At oral argument, the justices seemed split over where to draw the line for when police should seek a warrant to search a mobile device, and some seemed confused about modern social media applications.

Yet ultimately the high court was unanimous in its judgment. Roberts’ opinion embraced arguments long advanced by civil liberties groups about the need to reinterpret the Fourth Amendment in light of new technologies.

“The term ‘cell phone’ is itself misleading shorthand; many of these devices are in fact minicomputers that also happen to have the capacity to be used as a telephone,” Roberts wrote. “They could just as easily be called cameras, video players, rolodexes, calendars, tape recorders, libraries, diaries, albums, televisions, maps, or newspapers.”

Modern cell phones contain an incredible amount of information. At 16 gigabytes, the smallest iPhone model can hold a “football field’s worth of books,” according to a brief filed by the Center for Democracy and Technology and the Electronic Frontier Foundation. Nine out of 10 Americans, according to a survey by the Pew Center, own cell phones, and more than half – 55% – were identified as “smartphones.”

Cell phones, Roberts joked in his opinion, “are now such a pervasive and insistent part of daily life that the proverbial visitor from Mars might conclude they were an important feature of human anatomy.”