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Commentary: On privacy, the Supreme Court takes an uncertain step in the right direction

In its most recent term, the U.S. Supreme Court handed down one of the most important Fourth Amendment cases of the past several decades involving digital privacy. Chief Justice Roberts joined four justices to rule that the police must obtain a warrant before tracking a citizen’s location via his cell phone.

The case, Carpenter v. United States, involved a series of robberies that the FBI was able to tie to Timothy Carpenter after cell phone data showed he was near each of the robberies when they occurred. The FBI did not get a warrant for the data before obtaining it. The government argued that it can lawfully use cell phone data to track the location of any citizen at any time without a warrant.

The Supreme Court has now rejected that argument. In doing so, it has likely expanded protections for citizens’ privacy rights in a wide variety of new technologies, from emails to web browsers to home speaker systems like Amazon’s Alexa. But those protections remain uncertain and vulnerable to change. The court’s opinion was vague, and it focused on cell phone tracking alone. It pointed the way towards protecting privacy in the internet age without actually doing so. Although supporters of privacy should celebrate this important victory, we should not lose sight of how fragile it is.

The Fourth Amendment normally requires the government to have probable cause and a search warrant before searching houses or examining private data. But this principle has generally been limited by something called the “third party doctrine.” The third party doctrine dictates that personal information exposed to a third party like a phone company or a bank is no longer protected by the Fourth Amendment. In the internet era, the third party doctrine threatens to eliminate Fourth Amendment rights in almost every form of digital information. Google searches, emails, cloud-stored files, cell phone data and more are all shared with third party service providers.

The Carpenter decision seriously diminishes the power of the third party doctrine. Carpenter’s location data was exposed to his cell phone providers, Sprint and MetroPCS. Those companies recorded his location data in their own business records — companies often use this information for marketing and research. Yet the court ruled that this exposure to third parties no longer mattered for Fourth Amendment purposes. It was concerned about the almost unlimited potential of cell phone tracking to reveal things about citizens’ private lives. The court also noted that, in today’s world, people have little choice but to use cell phones and no ability to stop those phones from revealing their locations to their cell phone companies.

The court accordingly ruled that the third party doctrine does not extend to especially revealing forms of information, like cell phone data that can reveal a citizen’s every move. At first glance, this appears to be a narrow and fact-dependent ruling, one that depends on the uniquely revealing and unavoidable nature of cell phone tracking. But the principles of Carpenter extend to a wide variety of technologies.

Facial recognition and license plate tracking are similarly revealing of movement and similarly difficult for citizens to avoid. Web-surfing data, Google searches and speech recorded by Alexa are all extremely revealing forms of information and navigating the internet is certainly a necessary part of modern life. Protection for things like the contents of emails and text messages seems even more certain, as even many of the dissenting justices suggested that such writings are equivalent to the “papers” that the Fourth Amendment has traditionally protected. Because the logic of Carpenter extends to all of these technologies, it likely represents a huge victory for privacy despite its seemingly narrow focus.

In the end, the force of Carpenter will depend on the stability of the court’s personnel and the willingness of the chief justice to create clear rules to protect privacy rather than resolving cases with as little discussion of principles as possible. The court’s partial rejection of the third party doctrine represents a major victory for privacy rights. But the uncertainty and fragility of its holding means that the fight to preserve the Fourth Amendment in the internet age is far from over.

Matthew Tokson | University of Utah School of Law

Matthew Tokson (@mtokson) is an associate professor at the University of Utah S.J. Quinney College of Law who writes and teaches in Fourth Amendment law, among other subjects. He is a former senior associate at WilmerHale LLP and a former law clerk to Supreme Court Justices Ruth Bader Ginsburg and David H. Souter.


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