UPDATE, June 25: It's unanimous. In a 9-0 decision that came down this morning, the Supreme Court ruled that police need a warrant to search your cellphone. Here, the background on the case.

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Originally published on April 29, 2014.

The police don't need a warrant to look through your wallet for identification when they arrest you, and whatever they find in there—say, addresses of friends—is fair game. They would need a warrant, though, to go through your home computer, which is clearly something different, a place where you probably keep private and personal files. But what is your smartphone? A personal effect that you keep on you at all times? Or a drive full of personal data that should be protected from warrantless searches?

The answer could be "both," and that's why this tricky question of whether warrantless cellphone searches are legal is headed to the United States Supreme Court.

Today SCOTUS is hearing two cases on that theme, Riley v. California and United States v. Wurie, that had opposite outcomes in the lower courts. In the first case, police searched the phone of David Leon Riley after they arrested him but before they had a warrant. That evidence gleaned from the phone suggested Riley was involved in a gang and was admitted in his trial, and the gang involvement evidence led to a longer sentence, according to The Wire.

In the second case, a pre-warrant search of Brima Wurie's phone led police to find his home address. There they found guns, ammunition and drugs, which led to a 20-year sentence. However, an appeals court threw out parts of Wurie's conviction, saying that because the police shouldn't have looked through his phone without a warrant, the rest of the case could not stand up. Unsurprisingly, the Justice Department wants this decision overturned, writing a court brief that concludes: "Although cell phones can contain a great deal of personal information, so can many other items that officers have long had authority to search, and the search of a cell phone is no more intrusive than other actions that the police may take once a person has been lawfully arrested."

Any time digital privacy comes to the Supreme Court, two obvious points come to mind. First, that many of the laws on the books were drawn up by people who could not have foreseen this scenario, leaving the justices (who may or may not understand the technology) grappling with the interpretations of rules written with other technologies in mind. As The Verge points out, Judge Norman Stahl wrote in his decision in the Wurie case that, "The Court, more than thirty-five years ago, could not have envisioned a world in which the vast majority of arrestees would be carrying on their person an item containing not physical evidence but a vast store of intangible data."

Second: If the Snowden revelations didn't make this clear enough, the Justice Department is probably going to insist that whatever data is within reach is critical for law enforcement. To put it another way, don't sit around waiting for its lawyers to say, "nah, we don't need that information." PopMech contributor Glenn Harlan Reynolds argues for putting new laws on the books to protect our privacy rather than waiting for court rulings on laws from yesteryear.

With no protection, we're all going to be left with tough choices. Your phone is now powerful enough to become a pocket-sized extension of your brain, but should you keep it free of any information you might not want law enforcement to see? Lots of people have learned painful lessons about over-sharing over the last decade as social media has conquered the world. But we're not talking about users willingly giving away their information here. We're talking about what has become the gateway to your whole life, and whether officers can walk through it without a warrant.

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