Chief Justice John Roberts didn't hesitate last fall when a questioner asked him about the biggest constitutional challenge the Supreme Court faced.
Roberts told the audience at Rice University in Houston that the court must identify "the fundamental principle underlying what constitutional protection is and apply it to new issues and new technology. I think that is going to be the real challenge for the next 50 years."
The court has started the process, of course. In the recently completed term, a majority said technological advances in how quickly warrants may be obtained means that in most cases police officers must obtain one before forcing a suspected drunken driver to take a blood test.
And, over a sharply worded dissent from Justice Antonin Scalia, the court went a long way toward endorsing DNA testing as the modern-day equivalent of fingerprinting. It approved of Maryland's law that allows police to take DNA swabs at the time someone is arrested for — not convicted of — a major violent crime.
Now, amid a national debate over how much government should be able to find out about the private activities of its citizens in the name of combating terrorism, the next issue seems teed up for Supreme Court review:
More than 85 percent of Americans carry one and they provide authorities with more than just a vast record of a person's travels and phone calls. Modern smartphones have a memory capacity equal to that of a typical home computer in 2004, capable of storing millions of pages of documents.
"That information is, by and large, of a highly personal nature: photographs, videos, written and audio messages (text, email and voicemail), contacts, calendar appointments, web search and browsing history, purchases and financial and medical records," Judge Norman Stahl of the U.S. Court of Appeals for the 1st Circuit wrote recently. "It is the kind of information one would previously have stored in one's home."
Stahl wrote for the majority in a 2 to 1 decision that applied the Fourth Amendment to the search of a cellphone found on a man arrested for selling drugs. The amendment protects "the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures."
In most cases, a warrant is required. But the Supreme Court has said there are numerous exceptions to that general rule. In particular, in what courts refer to as "search incident to arrest," a warrantless search is justified when officers are protecting themselves by looking for weapons or securing evidence that might be destroyed.
And justices in the past have been lenient about allowing searches of items found on a person who has been legally arrested.
But Stahl and fellow Judge Kermit Lipez disagreed with the government's contention that a cellphone is "indistinguishable from other kinds of personal possessions, like a cigarette package, wallet, pager or address book, that fall within the search incident to arrest exception" approved by the Supreme Court.
Stahl and Lipez endorsed a "bright-line" rule that warrantless cellphone data searches are "categorically unlawful" given the "government's failure to demonstrate that they are ever necessary to promote officer safety or prevent the destruction of evidence."
Dissenting Judge Jeffrey Howard said his colleagues had no need to make such a broad ruling. "The constitutionality of a search cannot turn solely on whether the information is written in ink or displayed electronically," he wrote.
The decision creates a split among courts that have examined the issue. The Florida Supreme Court, for instance, has ruled that police generally may not search an arrestee's cellphone data, and some states have taken action legislatively.
But more importantly for the Supreme Court, every other federal appeals court that has looked at the issue is at odds with the 1st Circuit's decision in U.S. v. Wurie.
When the government asked for an en banc, or full court, review of the panel's ruling, 1st Circuit Chief Judge Sandra Lynch said there would not be much point in that.
"I think the preferable course is to speed this case to the Supreme Court," she wrote. Only the justices can settle the "confusing and often contradictory guidance to law enforcement" supplied by lower courts.
Once they've taken care of that, the justices might want to decide whether the government needs a warrant to obtain cellphone location data from telecommunications carriers. A panel of the U.S. Court of Appeals for the 5th Circuit in New Orleans ruled last month that a warrant was unneeded.
That contrasts with a unanimous decision from the New Jersey Supreme Court, based on the state constitution, that it is required. Other federal appeals courts are reviewing similar cases.
Tracking a person's whereabouts via a cellphone and searching it for information after an arrest raise different Fourth Amendment questions. But the justices know that a rapidly changing technology landscape complicates their work.
In a case last year concerning GPS tracking of a suspect, Justice Sonia Sotomayor worried about a digital age "in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks."
Justice Samuel Alito said "dramatic technological change may lead to periods in which popular expectations are in flux and may ultimately produce significant changes in popular attitudes."
In his Houston speech, Roberts said the coming decisions will test how "prescient" the framers were in developing a document that can deal with a world they could not have foreseen.
Roberts likes to be self-deprecating in public appearances, so he added that maybe he worried too much. "Maybe it's just the fact that technology is outpacing me rather than the Constitution," he said.