Supreme Court Recognizes Reasonable Expectation of Privacy in Historical Cell-Site Location Information

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The Supreme Court recently held in Carpenter v. United States that an individual has a reasonable expectation of privacy in historical cell-site location information (CSLI) that provides a comprehensive view of the individual’s movement. A 5-4 decision, Carpenter marks a significant development for both the third-party doctrine and in the privacy space more generally. Carpenter signals a change in the Court’s traditional view of the third-party doctrine and highlights the ubiquity and all-encompassing nature of CSLI in the process.

The petitioner, Timothy Carpenter, was convicted for his participation in a series of armed robberies. In order to obtain Carpenter’s CSLI during the investigation, the government sought and received court orders under the Stored Communications Act (SCA). At trial, the government presented the CSLI evidence alongside expert testimony. The expert witness explained that when cell phones tap into wireless networks, the wireless carrier generates a record with information on the cell phone’s approximate location based on the cell-site to which it connected. CSLI showed that Carpenter’s phone connected to cell sites near the sites of four of the charged robberies during the relevant timeframe.

Under the SCA, law enforcement can obtain a court order for records concerning an electronic communication service by offering “specific and articulable facts showing that there are reasonable grounds to believe that the contents of a wire or electronic communication, or the records or other information sought, are relevant and material to an ongoing criminal investigation.” 18 U.S.C. § 2703(d). However, Carpenter argued that the government’s seizure of CSLI violated the Fourth Amendment because he had a reasonable expectation of privacy in the CSLI and the government did not obtain a probable cause warrant.

The Court agreed with Carpenter, holding that the government’s acquisition of Carpenter’s CSLI was a Fourth Amendment search. While existing Fourth Amendment case law would permit the use of “augment[ed] visual surveillance” of an individual traveling on “public thoroughfares,” more “sweeping modes of surveillance” such as GPS and cell-site monitoring may raise constitutional concerns. Relatedly, while the well-established third-party doctrine draws a clear distinction between information that an individual discloses to a third party and information that an individual keeps private, the “detailed, encyclopedic, and effortlessly compiled” nature of CSLI warrants different treatment.

In other words, the Court called out an individual’s particular privacy interests in CSLI based on CSLI’s ability to provide “near perfect surveillance, as if it had attached an ankle monitor to the phone’s user” going back up to five years. The “detailed and comprehensive record” of an individual’s movements found in CSLI was “qualitatively different” than “telephone numbers and bank records,” two examples of records to which the third-party doctrine has previously been applied. The Court likewise recognized the changing nature of the underlying technology, the ubiquity of CSLI, and its retrospective nature in holding that Carpenter had a reasonable expectation of privacy “in the whole of his physical movements.”

Going forward, Carpenter raises as many questions as it answers. The Court ruled narrowly, citing the “unique nature” of CSLI, and did not assess whether any access to CSLI constitutes a Fourth Amendment search. The Court’s holding, which analyzed the substance of the information subject to access in recognizing a search, applies only to CSLI, and does not address questions of real-time access to CSLI or about information related to all phones connected to a cell site tower at a particular time. Carpenter could see many applications and challenges in Fourth Amendment cases involving government access to information. More broadly, because of the Court’s recognition of the unique privacy interest in this type of location data held by third parties, its reach could extend into other non-government privacy-related spaces.