U.S. Supreme Court justices signaled on Wednesday they may impose limits on the ability of police to obtain cellphone data from wireless providers to track the location of criminal suspects in a major test of privacy rights in the digital age.

During arguments in the closely watched case involving a convicted robber, several of the nine justices across the ideological spectrum indicated concern about the use of data revealing a suspect's past locations, based on the cellphone towers that relayed calls, without a court-issued warrant.

Liberal Justice Sonia Sotomayor sounded the alarm about the increasing amount of data that the government can potentially obtain, noting that most Americans "want to avoid Big Brother," referring to the symbolic all-seeing leader in George Orwell's dystopian novel "1984."

"They want to avoid the concept that government will be able to see and locate you anywhere you are at any point in time," Sotomayor said.

The court potentially could rule that the practice by law enforcement authorities of obtaining such data without a warrant amounts to an unreasonable search and seizure under the U.S. Constitution's Fourth Amendment. A ruling is due by the end of June.

Such a ruling would have a significant effect on law enforcement agencies that routinely request and receive this data from wireless providers in multitudes of criminal investigations as they try to link suspects to crimes.

The justices heard an extended 80-minute argument in an appeal brought by a man named Timothy Carpenter, convicted in several armed robberies at Radio Shack and T-Mobile stores in Ohio and Michigan with the help of past cellphone location data that linked him to the crime scenes. His American Civil Liberties Union lawyers have argued that without a warrant such data amounts to a Fourth Amendment violation.

The legal fight has raised questions about the degree to which companies protect customers' privacy rights. The big four wireless carriers, Verizon Communications Inc, AT&T Inc, T-Mobile US Inc and Sprint Corp, receive tens of thousands of these requests annually from law enforcement.

There is a possibility the court's four liberal justices could form a majority with one or more of the five conservatives, potentially including Chief Justice John Roberts and the court's newest member, Neil Gorsuch, who raised concerns from a property rights, rather than privacy rights, perspective.

The case was heard at a time of increasing concern among many Americans and lawmakers over surveillance practices of law enforcement and intelligence agencies.

Roberts mentioned a 2014 Supreme Court ruling he authored that required police in most instances to obtain a warrant to search a cellphone's contents when its user is arrested. Roberts reiterated what he said then, that smartphones packed with data-rich applications are ubiquitous.

When Trump administration lawyer Michael Dreeben, defending the use of the data without a warrant, said people can choose not to sign up for a phone, Roberts pounced.

"You really don't have a choice these days," Roberts said.


Sotomayor noted that people often have their cellphones at all times, including in bed. "It can be pinged at your doctor's office," Sotomayor said, and during the "most intimate details of your life, presumably at some point even in a dressing room as you're undressing."

Police helped establish that Carpenter was near the scene of the robberies by securing from his cellphone carrier his past "cell site location information," which tracks which cellphone towers relay calls. Carpenter's bid to suppress the evidence failed and he was convicted of six robbery counts.

Conservative Justice Samuel Alito said a ruling requiring a warrant "would be revolutionary" because it would upend longstanding precedent. Alito appeared concerned about setting new limits on the government's ability to obtain certain business records that authorities currently can get without a warrant, including bank records.

"Why is cell site location information more sensitive than bank records?" Alito asked ACLU lawyer Nathan Wessler, noting that bank records contain a wealth of information about debit card and other purchases.

The Supreme Court twice in recent years has issued major decisions concerning how criminal law applies to new technology, both times ruling against law enforcement, including the 2014 case Roberts mentioned. In 2012, the court also decided a warrant is needed to place a GPS tracking device on a vehicle.

The ACLU argued police need "probable cause," and therefore a warrant, to avoid a Fourth Amendment violation. The U.S. Justice Department said probable cause should not be needed to obtain customer records under a 1986 federal law called the Stored Communications Act.

Some justices disagreed on how much Americans know about the prevalence of cellphone data. Sotomayor said Americans do not know the extent of it, while 81-year-old Anthony Kennedy said even he knows how much customer data carriers possess.

"If I know it," Kennedy said, "everybody does."

(Reporting by Lawrence Hurley; Editing by Will Dunham)