In Carpenter v. United States, the U.S. Supreme Court recently held that the Fourth Amendment requires the government to get a search warrant to obtain Cell-Site Location Information (CSLI) from wireless carriers. CSLI reveals the location of a cell phone based upon the cell towers that the cell phone is using to obtain a signal. Carpenter marks an important and noteworthy change of course in Fourth Amendment jurisprudence.

The Carpenter decision is significant for a number of reasons.  First, the decision drastically alters the landscape of what information the government must obtain a search warrant for. Previously, a search warrant was generally not required in order to obtain transactional data in the possession of third parties. Second, the implications of the decision in Carpenter may be far-reaching. It remains to be seen what other information and records (e.g., metadata, real-time cell-site information, etc.) may fall within the purview of the decision.

The Carpenter decision may also have implications that extend beyond Fourth Amendment law into privacy regulation. While the FTC has long considered certain device-created tracking data to be more private than other types of information (e.g., Vizio), Carpenter may give additional ammunition for privacy advocates by elevating at least some longitudinal tracking data to Fourth Amendment-protected status. However, privacy scholars generally think about Fourth Amendment law as distinct from consumer-protection requirements because the purpose of the former is to protect individuals against nonconsensual government snooping, while the latter primarily serves to limit what companies can do with consumers’ data. Still, if law enforcement must obtain a warrant to access this data, privacy advocates may contend that companies should face increased restrictions on accessing other types of consumer data as well.

Expectation of privacy and third-party doctrine

The defendant, Timothy Carpenter, was convicted at trial of participating in a series of robberies following an investigation where FBI agents obtained 127 days of CSLI from Carpenter’s wireless carrier, via an order obtained pursuant to the Stored Communications Act (18 U.S.C. § 2703). The CSLI in question established that Carpenter’s phone was in the proximate area of several of the robberies in question.

Carpenter filed a motion with the District Court seeking to exclude the CSLI evidence because it was obtained without a search warrant. The District Court denied Carpenter’s motion and the Sixth Circuit Court of Appeals affirmed.

In its 5-4 decision, the Supreme Court overruled the District Court and the Sixth Circuit and held that a search warrant is required in order for the government to obtain CSLI. The opinion, authored by Chief Justice Roberts and joined by Justices Ginsburg, Kagan, Sotomayor, and Breyer, noted that CSLI “does not fit neatly under existing precedents,” and that “requests for cell-site records lie at the intersection of two lines of cases, both of which inform our understanding of the privacy interests at stake.” The first line of cases “addresses a person’s expectation of privacy in his physical location and movements.” The second line of cases stand for the proposition that “a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties.”

The majority stated that CSLI “is detailed, encyclopedic, and effortlessly compiled.” However, “[a]t the same time, the fact that the individual continuously reveals his location to his wireless carrier implicates the third-party principle of Smith and Miller.” Under those cases and others articulating the so-called “third-party doctrine,” the Court had previously held that a person forfeits their expectation of privacy when they disclose information to a third party. As a result, the government typically did not need to obtain a search warrant to access transactional information held by third parties.

In Carpenter, the majority declined to extend the third-party doctrine to CSLI, noting that “[g]iven the unique nature of cell phone location records, the fact that the information is held by a third party does not by itself overcome the user’s claim to Fourth Amendment protection.” Specifically, the majority held that “an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through CSLI.” The majority reasoned that “[m]apping a cell phone’s location over the course of 127 days provides an all-encompassing record of the holder’s whereabouts. As with GPS information, the time-stamped data provides an intimate window into a person’s life, revealing not only his particular movements, but through them his ‘familial, political, professional, religious, and sexual associations.’” Thus, when the government obtains CSLI, “it achieves near perfect surveillance, as if it had attached an ankle monitor to the phone’s user.”

The majority further reasoned that the third-party doctrine was inapplicable to CSLI because “[t]here is a world of difference between the limited types of personal information addressed in Smith and Miller and the exhaustive chronicle of location information casually collected by wireless carriers today.” As such, given the nature of the information sought, the majority held that a search warrant is required in order to obtain CSLI.

The majority did, however, note that its decision was “a narrow one” which only addressed the issue of historical CSLI. The decision did not call into question the application of the third-party doctrine to other types of business records and recognized that there may be certain case-specific exceptions that would not require a warrant (e.g., exigent circumstances).

Dissenting opinions

Justices Kennedy, Thomas, Alito, and Gorsuch all filed dissenting opinions. Justice Kennedy argued that, because the CSLI was in the possession of wireless carriers, the third-party doctrine should apply and no search warrant is necessary. Justice Alito agreed with Justice Kennedy, and he further argued that the Fourth Amendment has not previously applied to the compulsory production of documents. Justice Thomas argued that the Fourth Amendment should only protect searches of property, as opposed to a violation of a person’s “reasonable expectation of privacy.”

Justice Gorsuch, on the other hand, questioned the relative narrowness of the majority opinion, suggesting that the third-party doctrine needed to be revisited in a systemic manner. Justice Gorsuch reasoned that the specificity and detail of the data collected is irrelevant. Rather, he argued that CSLI data should be considered personal data and not third party data – similar to the case of Ex Parte Jackson (1878) which determined that a letter in the mail was the property of the author, not of the post office that held it, and therefore warranted a search.

This is a broad reading of the property rights and could have made the opinion even more significant had it been the majority. But this argument was not preserved by Carpenter’s legal team, so Justice Gorsuch ultimately dissented from the majority opinion rather than filing a concurrence on his preferred grounds.  Nevertheless, Justice Gorsuch’s opinion is important because it indicates that advocates for broader Fourth Amendment rights may pick up an additional vote if future litigants preserve this argument.

Antonia Ambrose contributed to this blog post.