Yesterday, the Supreme Court heard oral argument in Carpenter v. United States, a case involving the privacy of cell phone location information. At issue is whether the government violated the Fourth Amendment when it obtained 127 days of location data from the defendant’s cell phone provider without a warrant. And based on today’s argument, it would appear that a majority of the Justices think that it did. But there did not seem to be any consensus about why or how the Court should reach that conclusion, reasoning that could have broad implications for the future of privacy rights in the digital age.

It isn’t particularly surprising that warrantless, long-term location tracking would trouble at least a majority of the Court. In United States v. Jones, decided just five years ago, all nine Justices agreed that it was unconstitutional to attach a GPS device to a car and track it for 28 days without a warrant. But the Jones Court was also divided in its reasoning; Justice Scalia focused on the physical “trespass” of attaching a GPS tracker while Justices Sotomayor and Alito were concerned with the invasion of privacy. 

The important difference between Carpenter and Jones is the role played by a third party, the cell phone service provider. In Jones, investigators collected location data directly from the GPS device they secretly installed. But in Carpenter, the government requested historical cell phone location data from the phone company, which keeps records of where and when cell phones connect to their cell towers. The distinction matters because of the so-called “third party doctrine,” which dictates that there is no Fourth Amendment interest in information knowingly and voluntarily revealed to “third parties.” The doctrine comes from two cases, United States v. Miller and Smith v. Maryland, decided about 40 years ago. Miller concerned access to financial records held by a bank, and Smith involved access to telephone call records held by a phone company.

The big, unresolved question is how the Court will decide to handle Smith, Miller, and the third-party doctrine. The Court could overturn one or both of those cases, or more likely, it could limit them and decide that third-party doctrine doesn’t apply here. But to do that, the Court will need to craft a coherent rule explaining why. And at oral argument, it became clear that the Justices have very different thoughts about how to draw that line.

Justice Sotomayor, who expressed deep concern about the third-party doctrine in Jones, emphasized that the rule has never been absolute, pointing to the fact that a warrant is required to get the contents of phone conversations, even though the phone company is capable of eavesdropping. Likewise, Justice Breyer noted that a warrant is required to get medical records from a hospital and suggested a rule based on bodily privacy. Justice Ginsberg pulled at the distinction in Jones between long-term and short-term monitoring, whereas Chief Justice Roberts was concerned with whether the government should ever be able access to cell phone data without a warrant, drawing on the Court’s decision in Riley v. California that likened cell phones to “an important feature of the human anatomy.” Justice Gorsuch, perhaps channeling the late Justice Scalia, approached the issue from a property rights perspective and compared the government’s demands for data to the infamous “writs of assistance” that led to revolution and the Fourth Amendment.

Given the apparent variety of approaches, it would not be shocking if, as in Jones, there are multiple concurring opinions. But whatever path the Court chooses, it is sure to have ramifications for other types of personal data held by third parties, including data stored in the “cloud,” generated through third-party apps, or created by browsing the web. This was not lost on the Court, and least of all Justice Breyer, who remarked, “This is an open box. We know not where we go.”

At a minimum, the Court will need to resolve the third-party issue with respect to historical cell phone location records. But, as the Brennan Center for Justice urged in an amicus brief, the Court would do well to craft a broader rule that exempts all communications data from warrantless searches and seizures. Searches that implicate expressive and associational activities generally command heightened Fourth Amendment protection, and drawing a line based on that principle would make sense here, leaving the privacy of financial records for another day.

In any event, the theory that prevails in Carpenter is likely to have implications far beyond cell phone location information, even if the Court does not say so explicitly. As people live more and more of their lives online, the reach of the third-party doctrine will only grow and continue to generate new litigation unless the Court cuts it back here. The Justices seem ready to do so, but the open question is how.

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