Big Brother would have loved your smartphone. It not only knows where you've been and who's in touch with you but also records your photos, texts, emails and social media exchanges. Linked to the cloud, it allows access to your entire digital lifespan, including financial and medical records.
But can the police search your smartphone - that is, when they arrest you for, say, driving without a seat belt? There may not be a more important privacy question in our lifetimes, and Tuesday the U.S. Supreme Court heard argument on it.
The constitutional background here is pretty straightforward. The Fourth Amendment protects not only your person, but also your "papers and effects" against warrantless search. If you're arrested, there's an exception: The police can search for weapons within reach, and they can search for and seize any evidence on you "in order to prevent its concealment or destruction," according to a 1969 precedent. Under truly urgent circumstances - say, a ticking time bomb - police can ignore the warrant standards altogether.
Once the government has the evidence, it can look at any aspect of it, and also keep a copy. That tradition may well have made sense from 1789 until the invention of the smartphone. But given the tremendous quantity and quality of information we now carry with us, the Constitution will have to evolve.
The modern problem isn't just the profound invasion of privacy that's possible through a smartphone search. Much worse, under the old rules, the government could store all the data - including the stuff in the cloud - in an eternal government archive. Orwell might be surprised he never thought of it. (No carping from those of you who note that the National Security Agency already has more or less the same data. This archive would be different; it would be searchable by police.)
The good news from Tuesday's oral argument is that the justices seemed to realize our brave new world requires new rules.
Even the arch-originalist Antonin Scalia commented that if someone is arrested for not wearing a seat belt "it seems absurd that you should be able to search that person's iPhone."
The bad news is that there is no guarantee the court will do the logical thing and insist that a warrant ordinarily be required for searching a smartphone that has been seized incident to arrest. The court's conservatives seemed very interested in the rule proposed by the office of the solicitor general, which is that the police should be able to search a smartphone without a warrant in order to find evidence relevant to the crime for which a person is being arrested.
On the surface, the proposed rule has some mild appeal. It certainly responds to Justice Scalia's concern that every arrestee for any crime, no matter how small, could find his or her entire life's data reviewed and logged into a single government archive. The trick would be figuring out how to limit a data search to information related to the cause of arrest.
In the test case the court heard, the defendant was an alleged gang member, so the searches could logically include his emails, texts and photos, not to mention his bank account. His tattoos were part of the reason he was suspected of belonging to a gang, so records of visiting the tattoo parlor might have logically been included. Come to think of it, why not his medical records, in case he'd had a tattoo surgically removed?
As Justice Elena Kagan put it, "It sounds good as a limiting principle, but it ends up you can imagine in every case that the police could really look at everything."
As usual in close cases, the final disposition may come down to Justice Anthony Kennedy. Early in the arguments, Kennedy seemed interested in limiting the search possibility to serious crimes. This would help, but would not be anything close to enough; after all, the crime whose seriousness would be measured would not be one for which a person was convicted, but one of which he was merely suspected.
The arguments featured a final technological twist: One of the classic exceptions to the warrant requirement is to preserve evidence from destruction. Smartphones are distinctly susceptible to this risk insofar as most now include a feature that enables the owner to remotely wipe the phone of all data. Designed so that losing your phone doesn't mean losing your life, this feature could become your best friend if and when you're arrested.
During oral argument, the justices struggled over whether the danger of a wiped phone gave the police extra reason to search immediately. They speculated somewhat wildly about so-called "Faraday bags" and even "Faraday rooms," in which a phone could be turned on without receiving a cell signal and commanded to wipe data. Justice Sonia Sotomayor, cementing her new role as the court's techie, asked why police couldn't just put the phone in airplane mode and avoid the whole wiping problem.
In the end, the true privacy answer may lie in technology rather than constitutional law. I think I'll go out and get a phone that unlocks only to my fingerprint - and that automatically wipes if anyone else tries to open it.
That won't save me if the cops make me open it - remember the eyeball in "Blade Runner" - but I think in this case I won't count on the justices.
I'll rely on the engineers.
Noah Feldman, a Bloomberg View columnist, is a professor of constitutional and international law at Harvard.