TAP Scholars Explain the Impact of the Carpenter Decision on Privacy Law

By TAP Staff Blogger

Posted on July 17, 2018


Last month, the U.S. Supreme Court decided in Carpenter v. United States that the government generally needs a warrant in order to access a person’s cell site location information. Privacy advocates see this decision as a “groundbreaking victory for privacy rights in the digital age.” (ACLU attorney Nathan Freed Wessler, who argued the case before the court last November.) However, “former prosecutors and the four dissenting justices said the ruling threatens a major tool used by police and prosecutors in developing investigations.” (“Supreme Court Rules that Warrant Is Needed to Access Cell Tower Records,” The Washington Post)


Several privacy law scholars are hailing this decision as having “paradigm-shifting implications not only for Fourth Amendment law, but also for private-sector privacy law” (Margot Kaminski, University of Colorado) and “an inflection point in the history of the Fourth Amendment” (Paul Ohm, Georgetown University).


And still other privacy scholars express disappointment because the decision “only resolves a narrow issue and leaves many open questions” (Daniel Solove, George Washington University) or call the decision “incorrect” because it adds “another layer of confusion to the vexed law of unreasonable searches and seizures” (Richard Epstein, New York University).


Given that the opinions in the Carpenter decision total 119 pages, there is a lot to understand about the impact of the decision on privacy law and the Fourth Amendment. Fortunately, several TAP scholars are studying the decision, and sharing their thoughts in articles and blog posts. TAP is grateful that we have been granted permission to republish several of these articles, and we will do so over the next week.


Articles and posts by well-respected privacy law scholars are listed below. But first, a quick a walk-through of the basic points of the case.


A Primer on Carpenter v. United States


The case before the court was brought by Timothy Carpenter, prosecuted as a ringleader in a series of armed robberies in Michigan and Ohio. Cell tower information placed him at the robbery sites, and this information became damning evidence at his trial. The government obtained the cell site information under the Stored Communications Act. They complied with the statute, but the statute requires only reasonable suspicion and not probable cause. Carpenter appealed his conviction, contending that police unconstitutionally invaded his privacy without getting a search warrant first. (Thanks to NPR’s All Things Considered for the case summary, “In Major Privacy Win, Supreme Court Rules Police Need Warrant To Track Your Cellphone”.)


The key issues addressed in the decision are:

  • Expectation of Privacy – Did Carpenter have a right to keep his whereabouts private? Chief Justice Roberts acknowledged that in some of the court’s decisions prior to the digital era, the court had ruled that a driver should not expect his movements on public roads to be kept private. But, times have changed. People would not expect police to track their every movement over long periods of time, yet that is exactly what the cell-site location records do. Justice Roberts suggested that “because people carry their phones virtually everywhere with them, cell-site location records provide the government with near perfect surveillance, as if it had attached an ankle monitor to the phone’s user.”
  • Third-party Doctrine – Did Carpenter have a right to expect the data he shared with a third party (namely his cell phone location information that his carrier acquired) to be kept private? For decades, the Supreme Court has said that when you share your information with a third party, like a bank or telephone company, you lose the expectation that it will remain private. But the third-party doctrine evolved in the 1970s. Justice Roberts emphasized that cell-site location information is not a “garden-variety request for information from a third party” because of the “seismic shifts in digital technology that made possible the tracking of not only Carpenter’s location but also everyone else’s, not for a short period but for years and years.” At the time the third-party doctrine was established, he explained, no one could have envisioned that cellphones would be so ubiquitous and provide so much information about their users for so long. And, he added, because cellphones are such a pervasive part of life “that carrying one is indispensable to participation in modern society,” it can’t really be said that a cellphone user is voluntarily sharing information about his location with his carrier.

What the Scholars Are Saying


Paul Ohm
Professor of Law and Associate Dean for Academic Affairs, Georgetown University Law Center
The Broad Reach of Carpenter v. United States,” Just Security and republished on TAP with permission from Professor Ohm.


Carpenter v. United States is an inflection point in the history of the Fourth Amendment. From now on, we’ll be talking about what the Fourth Amendment means in pre-Carpenter and post-Carpenter terms. It will be seen as being as important as Olmstead and Katz in the overall arc of technological privacy.


Daniel Solove
John Marshall Harlan Research Professor, George Washington University School of Law
Carpenter v. United States, Cell Phone Location Records, and the Third Party Doctrine,” TeachPrivacy and republished on TAP with permission from Professor Solove.


The Third Party Doctrine has plagued Fourth Amendment jurisprudence for roughly 40 years. The Supreme Court should have overruled the Third Party Doctrine or at least carved out a greater chunk of it. Carpenter leaves open the door for more curtailment of the Third Party Doctrine in the future, but for now, it has left Fourth Amendment law needlessly unresolved and uncertain.


Richard A. Epstein
Laurence A. Tisch Professor of Law, New York University School of Law
Getting It Wrong On Cell Phone Searches,” Defining Ideas - A Hoover Institution Journal and republished on TAP with permission from Professor Epstein.


It is odd for the Chief Justice to go out of his way to tolerate a government search that is likely to lead to real abuse, while blocking well-conceived access of routine, non-confidential business records for no good reason at all. It is all too easy to claim that changed technological circumstances require scrapping old doctrines. But in this, as in so many other areas, that hasty conclusion is wrong. Get the conceptual foundations right the first time, and the resulting doctrine will prove more durable and sensible than the Chief Justice’s confused Carpenter decision. It is time for the Court to redo Fourth Amendment law from the ground up.


Margot E. Kaminski
Associate Professor of Law, Colorado Law, University of Colorado Boulder
Carpenter v. United States: Big Data is Different,” The George Washington Law Review and republished on TAP with permission from Professor Kaminski.


A central truism of U.S. privacy law is that if you share information, you do not have an expectation of privacy in it. This reasoning runs through both Fourth Amendment jurisprudence and privacy tort cases, and has repeatedly been identified as a central failing of American privacy law in the digital age.1 On June 22, in Carpenter v. United States,2 the Supreme Court did away with this default. While repeatedly claiming to be fact-bound and incremental,3 Chief Justice Roberts’s opinion has paradigm-shifting implications not only for Fourth Amendment law, but also for private-sector privacy law.


In short, the Court in Carpenter has declared that Big Data is different. Just how different remains to be seen.


Lior Strahilevitz
Sidley Austin Professor of Law, The University of Chicago Law School
The Path to Carpenter v. United States and Possible Paths Forward,” Concurring Opinions and republished on TAP with permission from Professor Strahilevitz.


An even bigger challenge for Justice Gorsuch will be to decide what kind of positive law matters. Baude and Stern are very clear that they would include not only property law but also tort law and general purpose statutes as legal content that informs the Fourth Amendment’s scope. Justice Thomas embraces the narrower conception (property law only) and it seems that Justice Gorsuch is inclined to go broader. But how much broader? … With the Court’s present composition, there are presumably going to be some cases where the Chief Justice parts company with the more liberal justices, and Gorsuch’s determination of how much positive law to include could prove decisive in a number of cases. Scholars like Baude, Stern, Richard Re, and others have made significant progress on those questions, but Gorsuch is someone who pays attention to what’s happening in legal academia, so this is a spot where contemporary scholars with big ideas can have a major impact.


Barry Friedman
Jacob D. Fuchsberg Professor of Law and Affiliated Professor of Politics, New York University School of Law
The Worrisome Future of Policing Technology,” The New York Times


But the 5-4 decision in the case, Carpenter v. the United States, should give you little comfort. The growing use of technology by law enforcement agencies to monitor or target people — particularly people and communities of color — is expanding at head-spinning speed, and nothing the courts do is going to stop that.


Orin Kerr
Frances R. and John J. Duggan Distinguished Professor of Law, University of Southern California Gould School of Law
When Does a Carpenter Search Start—and When Does It Stop?,” Lawfare


Accessing CSLI [cell-site location information] is a search, Carpenter reasons, because that has changed. Because technology has now made that kind of surveillance easy and potentially very common, the law needs to step in and make that surveillance difficult and rare again. As I have written before, this is the theory of equilibrium-adjustment. When technology dramatically expands the government’s power under an old legal rule, the thinking goes, the Court changes the legal rule to restore the prior level of government power. To ensure that the government doesn’t have unlimited power to catalog your movements over time, Carpenter holds that a search occurred and a warrant was needed. New technology means that you no longer have a reasonable expectation of privacy in your movements over time; the law gives back to you the reasonable expectation of privacy that you once had. The law giveth what technology taketh away.



Note: The Technology | Academics | Policy (TAP) website is sponsored by Microsoft Corporation. While Microsoft provides administrative and financial support for the site’s platform and content, there is no payment made to scholars for appearing or blogging on the site. That said, in the spirt of full disclosure, Microsoft joined other large U.S. technology companies in filing a brief in support of updating the Fourth Amendment for the digital era.



Recent TAP Bloggers