Richard Wolf

USA TODAY

WASHINGTON — Police pull up to a car outside a courthouse and see bomb-making materials and a man texting on his smartphone. That's a clear example of why cellphones should be subject to search, the Obama administration, state officials and police groups say.

Then police find a group of teenagers who appear inebriated, jaywalking and littering. All, of course, have smartphones. In such a case and nearly all others, privacy and criminal defense groups say, the phones should be out of bounds.

In the days of datebooks and diaries, the rules of the road for police searches during arrests were clear: They could examine the suspect and anything within reach, in order to locate weapons and preserve evidence. But the advent of cellphones and smartphones storing vast amounts of data has clouded the debate.

On Tuesday, the Supreme Court will be asked to clear it up. Judging from the justices' recent decisions, as well as the arguments presented by both sides, they may want to conjure up a compromise.

In just the past two years, the court has ruled that police can swab a suspect's cheek for DNA to put into an unsolved crimes database, as well as conduct strip searches of prisoners without reasonable suspicion. But it also has said police need a warrant to attach a GPS device to a suspect's car, to obtain blood from a drunk driver who refuses a breathalyzer test, and to bring a drug-sniffing dog up to the door of a suspect's house.

In most but not all such Fourth Amendment cases involving searches and seizures, Justice Antonin Scalia has joined the court's three female justices in demanding warrants, while Justice Stephen Breyer often has lined up with conservatives. Justices Anthony Kennedy and Clarence Thomas have been swing votes.

"As the text of the Fourth Amendment indicates, the ultimate measure of the constitutionality of a government search is 'reasonableness,'" Kennedy wrote in Maryland v. King, the DNA case.

The cellphone cases may be just a precursor to more expansive and potentially explosive high court inquiries. Among them: an examination of the National Security Agency's phone and computer surveillance methods, on which two federal district courts already have diverged.

TWO CASES RIPE FOR REVERSAL?

The two cellphone cases involve different crimes, different responses and different lower court rulings. What joins them is one salient fact: Police searched cellphones without first obtaining warrants.

A California court upheld David Riley's conviction on gang-related weapons offenses that police uncovered after stopping his car for expired tags, finding guns under the hood and then discovering incriminating photos and video on his smartphone.

In Massachusetts, a federal appeals court threw out Brima Wurie's conviction after a more limited search of his old-fashioned flip phone following a street arrest led police to find a cache of drugs and weapons at his home.

Because the California search was extensive and the Massachusetts search more limited and based on incoming calls, both cases could be ripe for reversal. But with appeals courts divided on the issue of cellphone searches, the justices are being asked to devise bright-line rules for police to follow.

That's particularly true because technology is advancing, creating new Fourth Amendment puzzles for police to solve. Nine in 10 adults in the U.S. own cellphones, more than half of them smartphones. Eight in 10 use those phones to send text messages; more than half send or receive e-mail, download applications, or access the Internet.

The least capable Apple iPhone 5 can store 800 million words of text, enough to line a football field with books or fill 16 flatbed trucks with paper. It can hold 8,000 photographs, 260,000 phone messages, or hundreds of home videos.

Combine that data with the estimated 12.2 million arrests made nationwide in 2012 — not including citations for traffic violations — and you have a potential perfect storm of cellphone searches.

"It is now common for drug deals to be arranged by cellphone, for violent street gangs to communicate through text messages, and for child abuse to be recorded on camera phones," the Justice Department says in its brief to the court.

Getting a warrant squanders precious time, it says, during which the phones can be "remotely wiped" of incriminating information. Gaetan Gerville-Reache, the lawyer for the police groups supporting the government's position, says the only way to preserve the data "is being able to do the search right then."

'ENTIRE LIVES ARE ACCESSIBLE'

Privacy groups say there's a solution for that: Seize the phones and put them in aluminum-lined containers called Faraday bags that can isolate them from outside signals. Even old-fashioned aluminum foil can do the trick until a warrant is requested, they say.

"Once the police have seized and secured a smartphone, there is no risk that the arrestee might destroy or alter its digital contents," says the brief from Stanford Law School's Jeffrey Fisher, the attorney for Riley.

But the risks for invasion of privacy are paramount, Fisher and the public defender representing Wurie argue. They are backed by a bevy of privacy and technology groups who fear government intrusion into Americans' private lives.

Fisher's brief calls smartphones "a portal into our most sensitive and confidential affairs." The DKT Liberty Project calls them "a window into a person's mind, goals, failures and successes." The Electronic Privacy Information Center says many users' "entire lives are accessible from their phones."

"Permitting warrantless searches of digitally-stored information will allow police to rummage through vast quantities of individuals' personal information — precisely what the Framers of the Fourth Amendment sought to prevent," says the brief from the Center for Democracy and Technology and the Electronic Frontier Foundation.

None of that is convincing to government officials seeking to stop crime and convict criminals. The brief submitted by California Attorney General Kamala Harris notes that people under arrest are not entitled to the same level of privacy as others. In Riley's case, it says, "the facts reflect only solid police work leading to a sound and just result."

Government and law enforcement groups have backpedaled a bit in their briefs. The police groups say police at least should be able to search "when they have reason to believe the phones contain evidence of past, present or future crime."

That won't work, privacy groups counter, because police will still need to rummage through the entire phone.

"It's not a very rigorous restraint," says William Jay, the attorney representing the American Library Association and The Internet Archive. "A phone is so capacious."