A majority of Supreme Court justices seemed to agree Wednesday that the abundance of private information available about Americans in the digital age might require new restraints on government's ability to access it.
In the specific case before the court, these new limits could require law enforcement officials to prove more to a judge about suspected criminal wrongdoing before they are able to collect cell-tower records, which can provide a detailed record of a person's whereabouts.
But the justices indicated that the explosion of digital information, which is transforming Americans' expectation of privacy, is raising a wide range of legal issues.
"This is an open box," Justice Stephen G. Breyer said. "We know not where we go."
Justice Sonia Sotomayor was the most insistent on protections. "Most Americans, I think, still want to avoid Big Brother," she said, while also acknowledging the public's increasing reliance on the modern technology that makes surveillance easier.
Deputy Solicitor General Michael R. Dreeben said that the government's use of cell-tower records, an important tool for solving crime, did not violate an individual's constitutional protection against unreasonable searches.
The records are kept by an individual's carrier, he noted, and in disclosing them the company is acting as a potential witness to a crime.
But Nathan F. Wessler, a lawyer for the American Civil Liberties Union, said the records serve as a "time machine" for law enforcement to reconstruct a person's minute-by-minute movements.
Wessler represents Timothy Carpenter, who is serving a 116-year sentence for his role in armed robberies in 2010 and 2011 at RadioShack and T-Mobile stores in and around Detroit — as part of a gang stealing smartphones.
One of the men arrested identified Carpenter as the ringleader who typically organized the robberies, supplied the guns and acted as a lookout. Authorities asked cellphone carriers for 127 days of records that would show Carpenter's use of his phone.
Such records indicate where a cellphone establishes connections with a specific cell tower and give a fair representation of the vicinity of the user. Wessler claimed new technology can be specific to an area about half the size of the justices' grand courtroom.
In Carpenter's case, the mass of information showed his phone at 12,898 locations, including close to where the robberies occurred when they took place.
Carpenter's attorneys say that the government's actions violated their client's rights under the Fourth Amendment, which protects against unreasonable searches. Authorities should have had to convince a judge that there was probable cause to get the records, they say.
Instead, under the Stored Communications Act, authorities had to meet a lesser standard, that there were "reasonable grounds to believe" that the records sought "are relevant and material to an ongoing criminal investigation."
The government contends that its actions fit squarely with the Supreme Court's prevailing precedents. In the 1979 decision in Smith v. Maryland, the court ruled that requesting records that showed the numbers called from a traditional home phone did not constitute what would be considered a "search" under the Fourth Amendment.
Because the caller's information was voluntarily transmitted to a third party — the telephone company — the caller had no reasonable expectation that the numbers called would remain private.
Wessler said Supreme Court precedents relied upon by the government were decided four decades ago.
"The court could not have imagined the technological landscape today," he said. In the future, he added, "highly sensitive digital records like search queries entered into Google, a person's complete Web browsing history showing everything we read online, medical information or fertility tracking data from a smartphone . . . would be vulnerable."
Justices Samuel A. Alito Jr. and Anthony M. Kennedy seemed most accepting of the government's arguments.
"I agree with you, that this new technology is raising very serious privacy concerns," Alito told Wessler, "but I need to know how much of existing precedent you want us to overrule or declare obsolete."
Kennedy disputed Wessler's assertion that most Americans don't know that they are creating lasting records of their whereabouts when they place calls.
"I think everybody, almost everybody, knows that," Kennedy said, getting a laugh when he added, "If I know it, everybody does."
But Chief Justice John G. Roberts Jr. said there was little Americans could do to avoid disclosing sensitive information. "You really don't have a choice these days if you want to have a cellphone," he said.
Dreeben noted that the case involved information about the routing of the calls, not about their content.
But Sotomayor voiced worries about the future. "As I understand it, a cellphone can be pinged in your bedroom. It can be pinged at your doctor's office. It can ping you in the most 10 intimate details of your life. Presumably at some point even in a dressing room as you're undressing," she said. "So I am not beyond the belief that someday a provider could turn on my cellphone and listen to my conversations."
Justice Elena Kagan indicated the court's concerns were a natural progression from recent cases involving technology. Five justices, she noted, had expressed concern about government's long surveillance of a suspect using a GPS device.
"The obvious similarity is that, in both cases, you have reliance on a new technology that allows for 24/7 tracking," she said.
But while the justices seemed to have a shared concern, there was little apparent agreement on the reasoning the court might use to justify a restriction of the government's access to the records.
Justice Neil M. Gorsuch, a conservative, seemed as concerned as some of the liberal justices about the government's ability to get the information.
He offered that the cell-tower records could be seen as Carpenter's property, and thus not available without a warrant, a proposal that did not seem to draw in other justices.
Dreeben said Gorsuch's proposal would be unlike any of the court's previous decisions. He urged the justices to go slowly.
"The technology here is new," he said, "but the legal principles that this court has articulated under the Fourth Amendment are not."
The case is Carpenter v. U.S.