Future-Proofing the Fourth Amendment

In Carpenter v. United States, Chief Justice John Roberts began the process of future-proofing the Fourth Amendment. In a majority opinion marked by technological sophistication and powerful arguments about arbitrary government surveillance, but overshadowed by four separate dissenting opinions, Carpenter both reframes the Fourth Amendment and reveals its fractured soul.

To understand Carpenter is to understand the fork in the road the Supreme Court faces confronting the digital age. Analog precedents point one way. Digital technologies point another. The constitutional path forward is unclear and no single Fourth Amendment theory controls. Carpenter forced the Court to make a choice about how to fit the Fourth Amendment into a world of digital surveillance.

The legal question in Carpenter was whether police needed a probable cause warrant to obtain cell-site location information (CSLI) from private cell phone company providers about the whereabouts of Timothy Carpenter. Mr. Carpenter had been suspected of being involved in a series of cell phone store robberies and (ironically enough) his personal cell-phone location data provided solid evidence that he was in the vicinity of the crimes. Police had applied for a court order under the Stored Communications Act to obtain the calls, but Carpenter argued that police needed a full probable cause judicial warrant to obtain this private location data consistent with the Fourth Amendment.

Writing for the majority, Chief Justice Roberts agreed with Carpenter, holding that the government’s acquisition of more than six days of cell-site records was a “search” for Fourth Amendment purposes. The Court reasoned that: “In light of the deeply revealing nature of CSLI, its depth, breath, and comprehensive reach, and the inescapable and automatic nature of its collection, the fact that such information is gathered by a third party does not make it any less deserving of Fourth Amendment protection.” In short, a government demand for a week’s worth of collected location data held by third parties is a “search” because it reveals private details of our lives and violates our reasonable expectation of privacy.

The majority opinion is notable for at least five separate reasons, each one of which might mark Carpenter as a blockbuster Fourth Amendment case.

First, Chief Justice Roberts institutionalizes the “digital is different” theme he initiated in Riley v. California (2014) that new technologies will not be controlled by analog legal precedents. Echoes of Riley (requiring a search warrant for smartphones incident to an arrest) reinforce how the Court understands the qualitative and quantitative differences in digital evidence. Signaling a new openness to expand the Fourth Amendment to fit digital criminal investigations, the Carpenter majority resisted a “‘mechanical interpretation’ of the Fourth Amendment” insisting that the “new,” “novel,” “unique,” “seismic” change in technologies warrants a different outcome. This recognition of digital transformation signals a new openness to ensure that the Fourth Amendment protects the digital lives of citizens.

Second, the majority reclaims the history of the Fourth Amendment as a bulwark against encroaching big data policing technologies. Harkening back to James Otis and the Framers, the Court positions the Fourth Amendment as a modern protective force “to secure ‘the privacies of life’ against ‘arbitrary power’” and “to place obstacles in the way of a too permeating police surveillance.” In an age of growing big data surveillance technologies capable of monitoring individuals and groups across entire cities, this systems update to the Fourth Amendment is a significant marker of the Court’s future intent.

Third, Carpenter signals the end of the third-party doctrine as traditionally understood. Up until Carpenter, the third-party doctrine held that any information shared with third parties (phone records, bank records) lost an expectation of privacy and thus protection of the Fourth Amendment. The majority distinguished the 1970s-era third-party doctrine cases of Smith v. Maryland and United States v. Miller as ill-suited for the modern age. While the Court did not overrule those cases, and, in fact, took pains to leave them intact, the third-party doctrine no longer applies automatically. In the specific context of cell-site records held by private parties, the Court reasoned, “the fact that the information is held by a third party does not by itself overcome the user’s claim to Fourth Amendment protection.” In other words, if a person “has a legitimate privacy interest in records held by a third party” then the Fourth Amendment requires a warrant to obtain that information. This is a dramatic and far-ranging protection in a world where most digital communications and most personal data is held by a third party. If cell-site records held by a third party implicate the Fourth Amendment then so do the other digital trails we leave behind.

Fourth, in choosing to frame the case as being about location data and the protection of individuals’ locational privacy in public, the majority dramatically expands the reach of the Fourth Amendment. The Court sees a danger in the government’s ability to conduct “near perfect surveillance,” giving police the power to “travel back in time to retrace a person’s whereabouts,” and allowing the creation of a “detailed chronicle of a person’s physical presence compiled every day, every movement, over several years.” Such a framing around locational privacy broadens the Fourth Amendment protection to all other digital technologies that also implicate locational privacy. After all, almost everything we do in the digital age – social media, internet searches, the Internet of Things – has locational privacy implications because they track location, and Carpenter suggests that they might also have Fourth Amendment implications.

Fifth, the majority creates a digital-Katz test for future surveillance technologies: Courts are to ask whether individuals have a reasonable expectation of privacy in personal data held by third parties. In the CSLI context, the Carpenter Court found a sufficient reasonable expectation of privacy in cell phone consumers’ location data to warrant Fourth Amendment protection. While perhaps not the model of clarity, a digital-Katz test emphasizes the importance of examining the specific technology at issue. In the cell-phone case, the Court seemed persuaded that because the data revealed too much personal information and because the cell signal was not voluntarily provided (the signals communicated automatically to the cell towers), on balance this particular CSLI technology violated an expectation of privacy. The Court left for another day questions about other technologies, such as real time CSLI collection or mass cell signal collection techniques, let alone future problems involving smart cars or facial recognition tracking.

Carpenter is the most important Fourth Amendment case of the 2017-18 Term and will undoubtedly change police practices and generate much new litigation for years to come. But, Carpenter is also notable for the fact that four Justices wrote four separate dissents, each of which could well have been the controlling opinion.

If Chief Justice Robert’s majority opinion was written for the future, Justice Thomas’ dissent was written from the past. In a radical break from fifty years of precedent, Justice Thomas suggested a wholesale rejection of Katz v. United States and the reasonable expectation of privacy test. The bulk of his dissent rehashes the muddled history of the reasonable expectation of privacy test and how an originalist vision of the Fourth Amendment would more properly focus on the textual language of “persons, houses, papers, and effects” – none of which would cover cell-site location information held by private companies. Calling Katz a “failed experiment,” Justice Thomas argues that it is time to “reconsider” the reasonable expectation of privacy theory and move back to a property-focused Fourth Amendment.

Justice Gorsuch also embraces a potentially Katz-less vision of the Fourth Amendment. Because this was the first test of Justice Gorsuch’s views of how new technologies should impact the Fourth Amendment many observers were eagerly awaiting his thinking. And readers got a lot of his thinking. In a lengthy and almost conversational exposition, Justice Gorsuch critiqued both the third-party doctrine and Katz, suggesting that the Supreme Court carve out a third way. In what will likely be the most discussed part of the dissents (if not the entire opinion), Justice Gorsuch hints at a positive law inspired approach to Fourth Amendment rules. What these positive law rules will look like, how property approaches will influence them, and how they apply to the digital age were teased without real resolution. Notably, Justice Gorsuch expressed skepticism of the third-party doctrine’s continued vitality in the digital age and criticized the underlying legal theories that have justified its use. While dissenting, he appeared to side with the majority’s intuition on the third-party doctrine’s impending demise.

Rounding out the dissents, Justice Kennedy wrote the most straightforward critique, arguing that the third-party doctrine controlled by Miller and Smith should also control CSLI business records, a position on third-party records that apparently no longer can claim majority support. Justice Alito wrote a thought provoking dissent arguing that the Court had unwittingly jeopardized the subpoena powers of law enforcement. In allowing Carpenter to challenge a lawful court order for private records, Justice Alito points out, the majority opinion also allows other suspects to challenge court orders (grand jury subpoenas, criminal subpoenas, administrative subpoenas) for records that they neither own nor control. If the Stored Communications Act order is the functional equivalent of a subpoena and (post-Carpenter) insufficient to obtain third party records, then that would mean that all similar records would also require a probable cause warrant (not a mere subpoena). If correct, this would curtail the current law enforcement practice to simply request personal information via subpoena.

As the most anticipated Fourth Amendment case in recent memory, Carpenter did not disappoint. The Court provided new theories of locational privacy, meditations on the convoluted path of privacy law, arguments to reconsider the prevailing Fourth Amendment doctrine, and more than a few loose ends for lawyers and law professors to puzzle through in the coming years. But, given a path to choose between the past and the future, the Supreme Court chose to bring the Fourth Amendment into the digital future and protect against growing technologically enhanced police surveillance powers.


The author co-authored the Brief of Scholars of Criminal Procedure and Privacy as Amicus Curiae in Support of Petitioner, No. 16-402 in Carpenter v. United States.

Read more at Harvard Law Review