The Supreme Court just ruled unanimously in two decisions that police officers can't search the cell phone of someone they've stopped or arrested unless they have a warrant. That's true even if the cops suspect that the phone has data that's relevant to the crime.
Police are already allowed to search "physical objects" that might be on a suspect's person — for example, in his pockets. But the key point in today's decisions was that (in the words of Chief Justice John Roberts, who wrote the opinion) there's a "qualitative and quantitative" difference between cell phones and other physical objects.
In other words, cell phones are different just because of how much information they can store or access, and because of how personal that information is.
The court even makes an oblique reference to sexting to make that last point, as Ryan J. Reilly pointed out on Twitter:
This is how SCOTUS refers to sexting: pic.twitter.com/ZGgeQvlSJl— Ryan J. Reilly (@ryanjreilly) June 25, 2014
The difference between the two cases was that only one of them (Riley v. California) involved a smartphone — the other (United States v. Wurie) involved a search of a "flip phone." Because "flip phones" can store a lot less data than cell phones, and aren't as likely to interact with external "cloud" servers to get data, it was possible that the Court might decide that they were closer to physical objects than digital ones.
But in fact, the Court decided, both phones had access to "digital data" that cops shouldn't have unrestricted access to.
Justice Sam Alito wrote a separate "concurrence" — which agrees with the outcome of the case, but not necessarily all the arguments Chief Justice Roberts used in the opinion.