WASHINGTON — In a major test of how to interpret the Fourth Amendment in the digital age, the Supreme Court on Tuesday will consider two cases about whether the police need warrants to search the cellphones of the people they arrest.
“The implications of these cases are huge,” said Orin S. Kerr, a law professor at George Washington University, noting that about 12 million people are arrested every year, often for minor offenses, and about 90 percent of Americans have cellphones.
The justices will have to decide how to apply an 18th-century phrase — the Fourth Amendment’s prohibition of “unreasonable searches and seizures” — to devices that can contain 100 times more information than is in the Library of Congress’ sprawling 72,000-page collection of James Madison’s papers.
The courts have long allowed warrantless searches in connection with arrests, saying they are justified by the need to protect police officers and to prevent the destruction of evidence. The Justice Department, in its Supreme Court briefs, said the old rule should apply to the new devices.
Others say there must be a different standard because of the sheer amount of data on and available through cellphones.
In February, for instance, the Texas Court of Criminal Appeals suppressed evidence found on the phone of a high school student who was arrested on charges of causing a disturbance on a school bus. “Searching a person’s cellphone is like searching his home desk, computer, bank vault, and medicine cabinet all at once,” the court said.
The justices are not always savvy about technology. At last week’s argument over whether an Internet streaming service was lawful, Justice Antonin Scalia seemed to think HBO was a broadcast channel rather than a cable channel.
But the justices can be sensitive to the implications of new technology for privacy rights, especially their own. Things did not go well for the Justice Department after one of its lawyers said at a 2011 argument that the FBI was free to place GPS devices on the justices’ cars. The government lost the case, against a drug dealer it had tracked for a month, by a 9-0 vote.
Similarly, in 2001, the court limited the use of thermal-imaging devices to peer into homes. Scalia, writing for the majority, said, “It would be foolish to contend that the degree of privacy secured to citizens by the Fourth Amendment has been entirely unaffected by the advance of technology.”
The problem in the thermal-imaging case, he wrote, was that the devices could detect not only heat lamps used to grow marijuana but also “at what hour each night the lady of the house takes her daily sauna and bath.”
Searches of phones may give rise to a similar protective reaction.
“It’s a technology that all the justices will understand,” Kerr said. “They all have cellphones.”
But they may not know how much information such phones can contain, including call records, messages, Internet browsing records, calendars, books, diaries, photographs and videos, to say nothing of applications that connect to financial, medical, and travel records.
Adam M. Gershowitz, a professor at William & Mary Law School, noted that his iPhone tracked and stored his movements. “I just looked,” he said, “and my phone shows that I arrived at work yesterday at 8:56 a.m.” It also showed where and when he had lunch.
The first case to be argued Tuesday, Riley v. California, arose from the arrest of David L. Riley, who was pulled over in 2009 in San Diego for having an expired registration. The police found loaded guns in his car and, on inspecting Riley’s smartphone, entries they associated with a street gang.
A more comprehensive search of the phone led to information that linked Riley to a shooting. He was later convicted of attempted murder and sentenced to 15 years to life. A California appeals court said neither search required a warrant.
In its Supreme Court brief, California said information on phones “is not different in kind from wallets, address books, personal papers, and other items that have long been subject to examination.”
Another case Tuesday, U.S. v. Wurie, involved a search of the call log of the phone of Brima Wurie, who was arrested in 2007 in Boston and charged with gun and drug crimes. The federal appeals court in Boston last year threw out the evidence found on Wurie’s phone.
“Today, many Americans store their most personal ‘papers’ and ‘effects’ in electronic format, on a cellphone, carried on the person,” Judge Norman H. Stahl wrote for a divided three-judge panel of the court, quoting the words of the Fourth Amendment.
News organizations filed a brief supporting Riley and Wurie in which they argued that cellphone searches can compromise news gathering.
Other briefs in the two cases focused to an unusual degree on the practical questions of whether phone searches must be conducted immediately or can await a warrant.
Officials in California told the justices that searches are required because cellphones can be used to set off bombs. Riley’s lawyers responded that “this scarcely resonates as an everyday concern.”
The state’s brief added that immediate searches are needed because data on cellphones can be erased by a remote signal, perhaps by criminal confederates. A supporting brief from several law enforcement groups described an application “that would wipe a phone’s memory based on when the phone is carried into certain locations — such as a police station.”
Riley’s lawyers responded that all the police need to do is put the seized phones in airplane mode while they seek a warrant.