As Ilya noted earlier, the Supreme Court struck a blow for privacy and the Fourth Amendment today. It ruled that a warrant is generally required when law enforcement officers want to search a cell phone they have seized. Justice Roberts’ opinion for a unanimous court provides some crisp language:

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.” (citation omitted) 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.

In this case, we pretty well knew we were going to get a win. So let’s set aside the trumpets and talk about the margin of victory. Did we get improvements in Fourth Amendment doctrine that will bolster privacy protection in cases to come? Only a little.

OK, let’s trumpet the case a bit. This is a unanimous case with a bright‐​line rule. It’s about the best outcome you could hope for in Riley and Wurie themselves (argued separately, decided together), and it’s a great vindication of the constitutional status of cell phones and our data on them.

Chief Justice Roberts seems to have brought the Court together on this one (save a niggling Alito concurrence) to produce a strong opinion that doesn’t show gaps among the justices. (They may all have felt a need to huddle, avoiding an open fight or the tipping of hands on the NSA spying controversy, for example.)

And on the major privacy controversy of the day, the Court did not tip its hand. It distinguished Smith v. Maryland, the case the government uses to justify gathering records about every U.S. phone. Smith held that using a pen register to gather phone calling information was not a search. “There is no dispute here that the officers engaged in a search of Wurie’s cell phone,” Chief Justice Roberts wrote, punting for the Court in this case based on the consensus among parties.

The errant decision in Smith relied on the “reasonable expectation of privacy” test arising from the 1967 case, Katz v. United States. The very good news from this decision is that the Court once again declined to use the Katz test in resolving a Fourth Amendment issue, as our briefs invited the Court to do (or not to do, as it were). Instead, the Court implicitly found that there were searches in both cases and that those searches were of persons, houses, papers, or effects. Then it examined the reasonableness of searching cell phones.

That’s important because it means that the Court is interpreting the Fourth Amendment more like a law and not as the stack of doctrines that I’ve previously called a “jumble of puzzles.”

Did the Court go all the way our way? Certainly not. The Court didn’t do the simplest thing we invited, which was to state explicitly that a cell phone is an “effect” under the Fourth Amendment. (It’s essential to the holding that a cell phone is an item protected by the Fourth Amendment, but the Court should have said so to model behavior for lower courts.) The Court also did not distinguish cleanly between “search” and “seizure,” which is a distinction that courts will have to navigate if they are to get right the harder Fourth‐​Amendment‐​and‐​technology cases.

There are delightful hints of our briefs’ influence on the case, though. (And what is this kind of write‐​up but an exercise in searching for—if necessary, inventing—your role in the development of the law?)

As our Wurie brief invited, the Court re‐​interpreted the decision in United States v. Robinson (1973) in a subtle but important way. Robinson approved the search of a crumpled cigarette pack owned by a person subjected to a traffic‐​related arrest. The Court incautiously granted a general right to search arrestees, including things they held which could have no relevant or destructible evidence and which created no risk to arresting officers. Since then, the Court has had to curtail the “container” doctrine that Robinson spawned.

Our brief commended the more granular analysis of searches and seizures that Justice Marshall had argued for in his Robinson dissent. Chief Justice Roberts was more granular with Robinson in this case, calling the examination of the cigarrette pack a “reasonable protective measure.” The idea of a general right to search arrestees, arising from Robinson, is further curtailed. There must be a constitutionally valid reason for going into an arrestee’s things.

The delightful (if contrived) ego‐​booster in the case, though, is the opinion’s reference to what use law enforcement may make of keys they acquire from an arrestee. In our Wurie brief, we emphasized that government agents had taken Wurie’s keys and used them to unlock the door of a home where they suspected he stayed. Inside the home at the time were a woman and her baby, who were not suspects in the case. While illustrating how keys applied to locks can be investigatory tools like cell phones when their electronics are activated, we also illustrated the gross extent to which the warrantless investigation of Wurie went—unlocking the door of a home behind which innocent Americans rested.

Using a cell phone to access cloud data, the Court wrote, “would be like finding a key in a suspect’s pocket and arguing that it allowed law enforcement to unlock and search a house.”

Whether Chief Justice Roberts or another justice picked up on our argument, we cannot know, but the decision used the key example to illustrate how possession of a tool or device does not allow any use of it law enforcement may wish to make.

There will need to be more cases that articulate details unexplored by the Court today, but the decision in Riley and Wurie are a solid vindication of the requirement that law enforcement wishing to examine the contents of cell phones must “get a warrant”—nice quote.