(CNN) The Supreme Court grappled with a major case involving privacy in the digital age on Wednesday, discussing how to apply established legal rules to rapidly changing technology.
Several of the justices struggled with the Trump administration's position that the government does not need a warrant when it seeks digital data from cell phones that reveal users' locations. Deputy Solicitor General Michael R. Dreeben stressed that individuals have diminished privacy rights when it comes to information that has been voluntarily turned over to a third-party, such as a phone company.
But while the justices pushed back on Dreeben's arguments, they didn't seem to all share the same rationale.
Justice Sonia Sotomayor, for example, said she feared a "dragnet sweep" on the part of the government and she noted that cell phones have become an "appendage" for people in the modern era. She noted that a cell phone can be pinged in bedrooms and doctor's offices.
"Most Americans, I still think, want to avoid Big Brother," she said. "They want to avoid the concept that government will be able to see and locate you anywhere you are at any point in time."
Other justices questioned whether they should draw a line based on the sensitivity of the data when considering what kind of information should trigger Fourth Amendment protections.
Justice Elena Kagan worried about long-term surveillance that she referred to as "24/7 tracking."
Chief Justice John Roberts seemed to disagree with the government's position that the collected information belonged to the cell service company and did not implicate the privacy of the customer.
"The person helps the company create the record by being there and sending out the pings," he said.
Justice Neil Gorsuch, alone, questioned whether the case should be decided on trespass grounds instead of taking a privacy-based approach.
Dreeben pushed back, telling the justices that while the technology is new, established legal protections are sufficient to deal with privacy concerns.
His arguments seemed to gain the most support from Justices Samuel Alito and Anthony Kennedy. Alito acknowledged the privacy concerns of new technology but he worried about existing precedent that the justices might "declare obsolete."
How the justices decide the case could provide a framework for other issues, including the future of the government's surveillance power. Privacy advocates say the case could impact everything from digital medical records and search queries on Google to smartwatch data.
Most courts have held that there is a diminished privacy interest when it comes to cell-site location data because the information has already been voluntarily provided to phone companies or third parties.
"This case is the first chance to start to set reasonable limits applicable to requests for these kinds of digital-age records by making clear that a warrant will sometimes be required," said Nathan Freed Wessler, an American Civil Liberties Union lawyer opposing the government in the case.
The controversy arose after a string of nine armed robberies were carried out at Radio Shack and T-Mobile stores in Michigan and Ohio.
One of the robbers, who confessed to the crimes, gave the FBI his cell phone number and the numbers of other participants in the scheme. Pursuant to the Stored Communications Act, a law that authorizes the government to obtain cell service providers' records under certain circumstances, the FBI obtained cell-site data for a Timothy Carpenter. The information -- over a range of 127 days -- placed Carpenter in the vicinity of the robberies.
Carpenter was later convicted of aiding and abetting the crimes, based in part on the location data.
Lawyers for Carpenter moved to suppress the cell-site evidence, arguing that the "reasonable grounds" standard necessary for the information under the federal law was too low a bar. Instead, they argued that the Fourth Amendment required the government to obtain a search warrant pursuant to a higher standard of "probable cause" before obtaining the data.
The Fourth Amendment protects the right of people to be "secure in their persons, houses, papers and effects, against unreasonable searches and seizures."
A federal appeals court ruled in favor of the government, holding that while the Fourth Amendment "protects the content of the modern-day letter," courts have not yet "extended those protections to the internet analogue to envelope markings, namely the metadata used to route internet communications, like sender and recipient addresses on email, or IP addresses."
The opinion, penned by Judge Raymond Kethledge of the US Court of Appeals for the Sixth Circuit, held that the business records in the case "fall on the unprotected side" of the Fourth Amendment.
The ACLU appealed the case to the Supreme Court on behalf of Carpenter and warned the justices of the privacy implications at stake.
"Allowing law enforcement to obtain such records free and clear of any Fourth Amendment restrictions would dramatically shrink the amount of privacy that people enjoyed from the time of the Framing through the dawn of the digital age," Wessler argued. He allowed that the government could obtain the information without a warrant for a time period under 24 hours, but after that, a warrant is likely necessary.
Dreeben countered in briefs that the petitioner "has no legitimate expectation of privacy in the business records his providers made of the cell towers used to route calls to and from his cell phone."
He wrote that "cell phone users are aware that they must be in a tower's coverage area to use their phones, and they must understand that their provider knows the location of its own equipment and may make records of the use of its towers."
Dreeben was making his first appearance back at the Supreme Court since he was detailed to work with special counsel Robert Mueller on the Russia investigation.
Nineteen states have filed a brief in support of the government, emphasizing that the cell-site data is general in nature. Lawyers for the states acknowledge, however, that other cases concerning "more sensitive data" could raise distinct concerns that should be addressed in future cases.
Roberts has long said that some of the court's most challenging cases involve applying long-held rules created by the courts to quickly developing technology.
In 2014, a unanimous court said that a warrant was needed in most cases before searching a cell phone. In 2012, the court had ruled on trespass grounds that longer-term GPS monitoring was a search triggering Fourth Amendment protections. But Sotomayor signaled in that case that the court might need to revisit court precedent holding that privacy rights are diminished if the information has already been turned over to a third party.
In court briefs, the ACLU said that from July 2015 to June 2016, AT&T received 75,302 requests for cell phone location information.
The case has attracted the attention of leading technology companies such as Facebook, Google and Apple. They have filed a brief in support of neither party in the case at hand, but instead they advise the court to "forgo reliance on" outmoded rules such as whether the information has been shared with a third party. They encourage a flexible doctrine with a focus on the sensitivity of the data at issue.
"The court should refine the application of certain Fourth Amendment doctrines to ensure that the law realistically engages with Internet-based technologies with people's expectations of privacy in their digital data," Seth Waxman, a lawyer for the companies, argued.
Fourth Amendment expert Orin S. Kerr, who will begin teaching at the University of Southern California in January, filed a friend of the court brief in support of the government in the case, arguing that the collection of historical cell-site data is unprotected by the Fourth Amendment and is the modern-day equivalent of information gathered from an eyewitness to suspicious conduct.
"On the one hand, the Fourth Amendment extends constitutional protections to a person's 'houses, papers and effects' from unwarranted government interference," he argued in court papers. "On the other hand, the Fourth Amendment offers no protection from government surveillance in public.
"Just as a person voluntarily exposes himself to observation by traveling in public to deliver communication, so does a person voluntarily expose himself to observation by hiring an agent to deliver his communications remotely."