What we know for sure on April 29, 2014: Approximately 90 percent of Americans have cellphones, including Justice Stephen Breyer. Twelve million people are arrested every year, the great majority of them for minor offenses.

What we don’t know for sure on April 29, 2014: Whether encryption is a serious problem for police officers attempting to search your cellphone; what, precisely encryption means (Justice Breyer describes encryption today as “some kind of system that once it goes ‘bzzz,’ you never can get the stuff again”); and what kind of cellphone Justice Breyer actually owns. As he explained it this morning, “I don’t know … because I can never get into it because of the password.”

Oral arguments in a pair of Fourth Amendment cases—Riley v. California and United States v. Wurie—reveal that, despite Breyer’s old man act, the justices are actually pretty savvy about the technology involved in cellphones, iPads, and tablets. What they are less certain about is how that technology will change in the very near future.

The Fourth Amendment prohibits the government from conducting “unreasonable searches and seizures.” But years of case law have established that the police can conduct a warrantless search at the time of an arrest to protect their own safety, or to prevent the destruction of evidence. In both cases today, the police searched a suspect’s cellphone in the course of an arrest (Riley, in California, had a smartphone; Wurie, arrested in Boston back in the Paleozoic era of 2007, had a flip phone). In both cases the phone searches led cops to evidence of much more serious crimes. Riley, who’d been stopped for expired tags, was eventually linked, by way of photos and videos on his phone, to a gang shooting and convicted on serious weapons and gang charges. Wurie was arrested for dealing drugs, but a police search of his call log led the cops to his home where piles of more drugs were found. The California courts sided with the police in Riley’s case; in Boston, a federal appeals court sided with Wurie. The question in each case: Can the police search your phone, without a warrant, any time they arrest you?

The problem for the court today is that they don’t much like the prospect of allowing the cops to search jaywalkers’ cellphones for evidence of anything bad they’ve ever engaged in. Even Justice Scalia conceded that for someone arrested simply for driving without seat belts, “it seems absurd that they should be able to search that person’s iPhone.” But at the same time, the justices also don’t want to hamstring the police who claim that if they can’t search cellphones, they will be in danger, and major crimes will go unsolved. There is little attempt to try to cram these facts into the James Madison time machine. No talk of tiny constables, as we heard in the GPS case. Most of the court agrees that there is no way the framers could have anticipated this “new world,” as Justice Kennedy describes it: a world in which “the fact that someone arrested for a minor crime has their whole existence exposed on this little device.”

Stanford Law School’s Jeffrey Fisher represents Riley in the first case, and as he explains to the justices, the Framers denied police officers authority “to search through the private papers and drawers and bureaus and cabinets of somebody’s house, and that protection should not evaporate more than 200 years after the founding” because technology has given Americans the ability to “carry that information in their pockets.”

Justice Samuel Alito asks Fisher, “What if your client was an old-school guy and he didn’t have a cellphone. He had a billfold and he had photos that were important to him in the billfold. Do you dispute the proposition that the police could examine the photos in his billfold?” Fisher concedes that this would be a permissible search, in part to search for a razor or pin that could be used to hurt the officer. But a phone is different, he presses, because “digital information … implicates vast amounts of information, not just the photos themselves, but the GPS locational data that’s linked in with it, all kinds of other information that is intrinsically intertwined in smartphones.” This, notes Fisher, is why the police should have to get a warrant, as they do for other searches. Fisher adds that “it’s not just what can be looked at; it’s how it can be kept. … My understanding in California is, at least for some crimes, it’s not just that they’re downloading the information … they’re keeping this information in ever-growing databases of every cellphone that they’ve ever seized.”

Justice John Roberts evinces a keen understanding of the workings of Facebook, Twitter, Fitbit, and other apps. Fisher tells him that Fitbit raises the same issues as the thermal imaging system that worried the court in an earlier drug case, when it ruled that cops scanning a home with infrared technology and no warrant violated the Fourth Amendment: “Modern smartphones,” Fisher explains, “work the inside of people’s house. They work the appliances and—and they have cameras. They also monitor the inside of people’s bodies.” Justice Anthony Kennedy wonders why the most recent discussion of whether cops can search someone’s briefcase and diaries comes from a 1916 case. Fisher has an answer: “The reason I think you don’t find [diaries] is because people hardly ever carry a diary outside the home with them. It was kept in a private drawer in the bedroom.” He contrasts this with “the modern reality of smartphones,” which are “an indispensable item for everyday life.” Justice Scalia asks Fisher if the cops can answer the phone if it rings in the middle of an arrest. Fisher says yes.

California’s Solicitor General Edward DuMont rises to defend the right of cops to search your phone when they arrest you. He says there is no difference between the police searching the paper pictures in your pocket and the digital photos on your phone. Justice Elena Kagan stops him right there: “A person can be arrested for anything. A person can be arrested for driving without a seat belt. And the police could take that phone and could look at every single email that person has written, including work emails, including emails to family members, very intimate communications, could look at all that person’s bank records, could look at all that person’s medical data, camera … GPS. … Now, that strikes me as a very different than the kind of world that you were describing where somebody has pictures of their family in a billfold. Doesn’t it strike you that way?”

DuMont insists that this sort of cellphone use is “marginal” but Kagan stops him. “You call it marginal, but, in fact, most people now do carry their lives on cellphones, and that will only grow every single year as, you know, as young people take over the world.”

Chief Justice John Roberts asks DuMont, “Is there any basis for the generality that there’s a safety concern? Do you have a case, not where the phone exploded, but when the phone was used to trigger a device or anything like that?” DuMont says no. Then he loses the NRA vote when he describes a case in which a cellphone photo of the driver standing arms akimbo with his assault rifles justified a police search to protect the officer’s safety. DuMont keeps talking over Kagan until the chief justice gets mad. Breyer asks DuMont to choose a rule for the court: The first is that cops always need a warrant to search a smartphone, the second is that they never need one. The third? “Sometimes yes, sometimes no.” DuMont chooses door No. 3, but Breyer persuades him to fess up and change it to the second—they never need one.

The justices, on the other hand, seem to be leaning toward door No. 3: some rule that lets the cops search cellphones in serious cases but not for jaywalking. Justice Kennedy suggests that the “distinction ought to be between serious and non-serious offenses.” Alito suggests the rule could be that you need no warrant to search for something with “a close analogue in the digital era to something that would have been allowed in the predigital era.” And Justice Scalia suggests that you could search a phone without a warrant “for evidence of the crime of arrest.” As he explains, “That will cover the bad cases, but it won’t cover the seat belt arrest.”

Kagan seems mystified that the new constitutional rule may be that “one has to keep one’s cellphone at home to have an expectation of privacy in it?” Because doesn’t that make it a home phone? And Breyer then inexplicably admits that he carries around a paper GPS system: “I don’t want to admit it, but my wife might put a little note in my pocket.”

Next comes Deputy Solicitor General Michael Dreeben, who sides with the police searches and introduces several variations on the “bzzz” argument: that bad guys can wipe their phones remotely, lock their phones remotely, and signal their confederates remotely, all creating an exigent need for the police to search phones instantly upon arrest. There is some talk of something called a Faraday bag, in which cops can store phones to stave off remote zapping, but, Faraday or no, Dreeben insists that the police need to search your phone right now. Sotomayor asks why the cops can’t just set the phone to airplane mode and get a warrant. The answer is: No!

Dreeben will go on to argue the second case, about flip phones, which principally raises the constitutional question of why the court agreed to hear a case about flip phones. (It’s certainly possible that Justice Breyer has one, and just can’t figure out the password.) Either way, the Wurie case goes poorly for the Fourth Amendment, raising some possibility that the searches are to be deemed legal on flip phones and illegal on smartphones. Either way, the justices acquit themselves remarkably well both on the technology front, and in understanding how fast the technology is moving. They appear to be trying to craft a constitutional compromise that fully appreciates that what we carry around in our back pocket is more substantial than Thomas Jefferson’s entire library, and also that criminals can’t be allowed to hide behind new technologies, as the law struggles to catch up.