On Wednesday, the Supreme Court heard oral arguments in Carpenter v. U. S., a case that involved the collection of 127 days of Petitioner Thomas Carpenter’s cell site location information as part of an investigation into several armed robberies. We attended the argument to gain any insights into how the Supreme Court may resolve this important case.

The central issue in the appeal is whether the government can access this type and amount of individual location data without a warrant. But an equally important issue is whether the Supreme Court should reevaluate the “third-party doctrine” exception to the Fourth Amendment’s warrant requirement in light of dramatic changes in the way individuals interact with technology in the digital era. The “third-party doctrine” provides that individuals have no expectation of privacy in any information that is voluntarily released to a third party—a mobile-phone provider, cloud service provider, and the like. The Court’s decision will have major implications for technology companies’ ability to protect customer data against warrantless searches by law enforcement officials.

During the 80-minute, extended oral arguments, the Justices broadly acknowledged that technology has changed dramatically in the decades since the Court originally recognized the third-party doctrine. Each Justice, however, appeared to place varying weight on the import of that change on current legal standards. Justices Kennedy and Alito focused on the information itself, rather than the technology, asking whether location information should be considered more sensitive than the bank information that United States v. Miller permitted law enforcement to access without a warrant, suggesting that banking information might be considered more sensitive.

Justice Breyer, by contrast, referred to this sort of cellphone location information as “highly personal information” and that “on a line . . . it’s somewhat closer to the [protected] diagnostic testing than it is to purely commercial information.” Justice Sotomayor shared in this assessment, further noting her discomfort with the large scope of information cell phones are capable of collecting, and the implications of allowing this sort of information to go unprotected. She stated that she is “not beyond the belief that someday a provider could turn on [her] cell phone and listen to [her] conversations.” Thus, by implication, cell phone information is of a nature that must be protected from law enforcement intrusion, otherwise the government would have open access to monitor individual’s activities in bed, in the bathroom, and in other intimate, private locations.

Justice Sotomayor repeated her concerns that “[t]he Constitution protects the rights of people to be secure. Isn’t it a fundamental concept . . . that that would include the government searching for information about your location every second of the day?” She noted the desire of the American people to “avoid Big Brother,” and explained that the third party doctrine “was never an absolute rule,” and has been subject to many limitations over the years. Justice Kagan also noted the similarity between this case and United States v. Jones, which found that a warrant was required to put a GPS tracking system on a car (albeit under a trespass theory). She said that the key issue in both is the “reliance on a new technology that allows for 24/7 tracking” and introduces “an altogether new and different thing” to “intrude on people’s expectations of who would be watching them.”

The government contends, however, that these law-enforcement demands are simply asking businesses to provide information about their own transactions with customers, and are not subject to Fourth Amendment protections. The crux of the government’s argument rests on the assumption that individuals voluntarily choose to use cellphones; that cellphones, by their very nature, relay location information to cell towers; and that cell services providers “choose to make their own business records” of that location information without mandate by the government.

Justice Roberts noted that the Court’s decision in Riley v. California has already settled individuals’ lack of meaningful choice in whether to engage with these technologies, but noted that it is an open question whether the information at issue here is sufficiently sensitive to be analogous to protected “content” (requiring a warrant for access) or to non-content “routing information” (which does not require a warrant). Justice Kennedy joked that if he knows that business have this cell phone data, everybody does. But other justices were more reserved in previewing their opinions on whether consumers have a reasonable expectation of privacy in location information. Justice Gorsuch, for example, questioned the government’s conclusion with wariness, saying “it seems like your whole argument boils down to if we get it from a third-party, we’re okay, regardless of property interest, regardless of anything else. ” Justice Roberts echoed this hesitation by clarifying again the government’s assertion “that so long as a third party’s involved, we can get anything we want.” Without revealing where they believe a line limiting the third-party doctrine should be drawn, both Justices implied that a line should be drawn somewhere.

The main focus of the Carpenter arguments centered on where the line in limiting this doctrine should be drawn, and how to draw this line in a way that will be effective as technology progresses further beyond what we can imagine today. Although the Justices appear divided on exactly where to draw this line, most recognized that the legal standard should take into account how the vast changes in the technological landscape affect people’s expectation of privacy and how continued changes will only further augment those effects.

We will, of course, report on the Carpenter decision when it is released.