WASHINGTON -- Police usually must get a warrant before searching the mobile phone of a person being arrested, the U.S. Supreme Court ruled Wednesday, saying the vast trove of information on modern devices requires broad constitutional protections.

The unanimous decision came in two cases that tested the reach of privacy rights in the digital age. More than 90 percent of American adults own mobile phones, giving the ruling broad practical significance.

"Modern cellphones are not just another technological convenience," Chief Justice John Roberts wrote for the court. "With all they contain and all they may reveal, they hold for many Americans the privacies of life."

The disputes, which tested the Constitution's Fourth Amendment and its ban on unreasonable searches, were part of a wider debate over electronic privacy that some experts expect to ultimately produce a Supreme Court showdown over the National Security Agency's telephone-data surveillance program.

Lower courts had reached different conclusions on cellphone searches, with some saying police can constitutionally look through a phone just as they can search other objects in the person's possession at the time of arrest.

Earlier Supreme Court decisions from the 1970s -- when cellphone technology was not yet available -- allowed police to empty a suspect's pockets and examine whatever they found to ensure officers' safety and prevent the destruction of evidence.

But Roberts said there's no comparison between cellphones and packages of cigarettes and other items that were at issue in the earlier cases.

A ride on horseback and a flight to the moon both "are ways of getting from point A to point B, but little else justifies lumping them together," he said.

"Many of the more than 90 percent of American adults who own a cellphone keep on their person a digital record of nearly every aspect of their lives -- from the mundane to the intimate," Roberts wrote.

Even the word "cellphone" is a misnomer, he said.

"They could just as easily be called cameras, video players, Rolodexes, calendars, tape recorders, libraries, diaries, albums, televisions, maps or newspapers," he wrote.

Roberts acknowledged that the decision would make law enforcement more difficult.

"Cellphones have become important tools in facilitating coordination and communication among members of criminal enterprises, and can provide valuable incriminating information about dangerous criminals," he wrote. The case united the nine-member court, with only Justice Samuel Alito adding so much as a qualification. Alito, who agreed with Roberts on the result and some of his reasoning, wrote separately to say he would reconsider the matter if Congress or a state legislature drafted a law that made distinctions based on the type of information being sought.

One of the cases before the Supreme Court involved an old-style "flip" phone with limited data capacity, while the other concerned a newer smartphone.

The smartphone case, Riley v. California, 13-132, stemmed from David Leon Riley's 2009 arrest in San Diego for carrying concealed and loaded weapons under his car's hood. Police took Riley's Samsung Instinct M800 smartphone, searching it at the scene and later at the station.

Officers found photos and videos suggesting that Riley was a member of a gang, as well as a photo of him and another person in front of a car that police suspected of being involved in a shooting. The information eventually helped prosecutors win a conviction against Riley on shooting-related charges, including attempted murder.

Riley was sentenced to 15 years to life in prison, and a California appeals court upheld the conviction. His case now returns to a lower court.

President Barack Obama's administration told the justices that police need to be able to search smartphones immediately, before accomplices can wipe the data from a remote location. During arguments in April, a government lawyer also said new technology can automatically encrypt data when a phone shuts off, making it impossible for police ever to get access.

Roberts said the briefing in the case "reveals only a couple of anecdotal examples of remote wiping triggered by an arrest." He added, "Similarly, the opportunities for officers to search a password-protected phone before data becomes encrypted are quite limited."

The chief justice also said police can use aluminum-foil "Faraday bags," which can isolate a phone from radio waves and prevent the destruction of data from the outside.

"We cannot deny that our decision today will have an impact on the ability of law enforcement to combat crime," Roberts wrote. "Privacy comes at a cost."

In the flip-phone case, United States v. Wurie, 13-212, the Obama administration sought to reinstate the conviction of Brima Wurie, who was arrested in 2007 in Boston on drug charges.

At the police station, officers saw that Wurie's phone was repeatedly receiving calls from a number identified on the caller-ID screen as "my house." An officer opened the phone, checked the call log and found the number for the house.

Police then used that number to get Wurie's address. Officers eventually found crack cocaine, marijuana and a firearm in his apartment. A jury convicted Wurie on drug and weapons charges, and he was sentenced to more than 21 years in prison.

A federal appeals court overturned the conviction, saying police had violated Wurie's constitutional rights. The Supreme Court upheld the lower court ruling.

The Justice Department said Wednesday that it will work with law enforcement agencies to ensure compliance with the ruling.

"We will make use of whatever technology is available to preserve evidence on cellphones while seeking a warrant," said Ellen Canale, a department spokesman.

The department will also help agents determine "when exigent circumstances or another applicable exception to the warrant requirement will permit them to search the phone immediately without a warrant," she said.

Privacy advocates declared the Supreme Court decision a big step forward.

"Today's decision is a huge win for individual privacy," said Sen. Ron Wyden, an Oregon Democrat who serves on the Senate Intelligence Committee. "I aim to use this decision as a springboard to secure greater privacy rights in the days ahead."

Ilya Shapiro, a senior fellow in constitutional studies at the libertarian-leaning Cato Institute, said the ruling "means that being arrested for, say, not paying a speeding ticket will no longer open you up to having your entire life examined by law enforcement."

Information for this article was contributed by Greg Stohr of Bloomberg news; by Adam Liptak of The New York Times; by Mark Sherman, Nancy Benac and Raphael Satter of The Associated Press; and by Michael Doyle of McClatchy Newspapers.

A Section on 06/26/2014