WASHINGTON — The Supreme Court decided 40 years ago that police don't need a search warrant to look through anything a person is carrying when arrested. But that was long before smartphones gave people the ability to take with them the equivalent of millions of pages of documents or thousands of photographs.

In a new clash over technology and privacy, the court is being asked to resolve divisions among federal and state courts over whether the old rules should still apply in the digital age.

The justices could say as early as Friday whether they will hear appeals involving warrantless cellphone searches that led to criminal convictions and lengthy prison terms.

There are parallels to other cases making their way through the federal courts that challenge the massive collection without warrants of telephone records by the National Security Agency. In both situations, the government is relying on a Supreme Court decision from the 1970s, when most households still had rotary-dial telephones.

Cellphones are now everywhere. More than 90 percent of Americans own at least one, the Pew Research Center says, and the majority of those are smartphones — essentially increasingly powerful computers that are also telephones.

In one of two cases before the justices, the federal appeals court in Boston threw out evidence police found when they conducted a limited search of a suspected drug dealer's cellphone after his arrest. Judge Norman Stahl of the 1st U.S. Circuit Court of Appeals said warrantless cellphone searches create a serious threat to the privacy even of people who have been properly arrested.

"Today, many Americans store their most personal 'papers' and 'effects' in electronic format, on a cellphone, carried on the person," Stahl said.

Under the Fourth Amendment, police generally need a warrant before they can conduct a search. The warrant itself must be based on "probable cause," evidence that a crime has been committed, the Constitution says.

But in the early 1970s, the Supreme Court carved out exceptions for officers dealing with people they have arrested. The court was trying to set clear rules that allowed police to look for concealed weapons and prevent the destruction of evidence. Briefcases, wallets, purses and crumpled cigarette packs all are fair game if they are being carried by a suspect or within the person's immediate control.

Car searches pose a somewhat different issue and in 2009, in the case of a suspect who had been handcuffed and placed in the back seat of a police cruiser, the court said police may search a car only if the arrestee "is within reaching distance of the passenger compartment" or they believe the car contains evidence relevant to the crime for which the person had been arrested.

There is growing division in state and federal courts over whether cellphones deserve special protection. At least six courts have allowed warrantless searches, and at least three have not, said Stanford University's Jeffrey Fisher, representing a California defendant whose case is the other one being considered by the Supreme Court.

The California case might attract the court's attention because it involves a more extensive search of a smartphone.

Things quickly went from bad to worse for Fisher's client, David Leon Riley, when a San Diego police officer pulled over Riley's Lexus for having an expired registration. In quick succession, police learned Riley's license was suspended, decided to impound the car and found loaded guns under its hood. Riley was arrested.

An officer looking at Riley's Samsung smartphone saw that some words normally beginning with the letter K were preceded by the letter C. Police say the notation CK signifies "Crip Killers," a slang term for members of a gang known as the "Bloods."

Hours later at a San Diego police station, a detective examined the phone more closely, finding videos and pictures providing more evidence of Riley's gang affiliation, including one showing he may have been involved in a gang-related shooting. A photograph showed Riley posing in front of a red Oldsmobile police suspected was used to flee the scene of a shooting. It turned out Riley owned the red car, and tests confirmed that the guns seized from the Lexus were used in the shooting.

Indicted for attempted murder and other charges, Riley was convicted and sentenced to a term of 15 years to life in prison. At no time did police seek a warrant to search his smartphone.

In the Boston case, Brima Wurie emptied a set of keys, $1,275 in cash and two cellphones from his pockets when he arrived at a Boston police station for processing in September 2007 after his arrest on suspicion of selling crack cocaine.

Police eventually examined the call log on his flip phone and used the information to determine where he lived. When they searched his home, armed with a warrant, they found crack, marijuana, a gun and ammunition. The evidence was enough to land him more than 20 years in prison.

The Justice Department is appealing the 1st Circuit ruling that threw out the evidence against Wurie, encouraged by a judge who dissented from the decision and a second who wanted to speed the issue along to the high court.

"Only the Supreme Court can finally resolve these issues, and I hope it will," Chief Judge Jane Lynch wrote.

Follow Mark Sherman on Twitter @shermancourt

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