In 2010, the FBI sought to arrest the “High Country Bandits,” two men engaged in a rural bank robbing spree. Law enforcement could not see the Bandits’ faces in surveillance videos, but a witness saw one of them use a cell phone during a robbery. To identify the suspects, the FBI sought four “cell tower dumps” from cell carriers, collections of the phone numbers “from all the devices that connected to a cell site during [the] particular interval” in which four of the robberies occurred. In the case of the High Country Bandits, the cell tower dumps returned the cell-site location information (CSLI) of 150,000 cell phone numbers, only two of which—the Bandits’ numbers—appeared near all four robberies.

This type of warrantless governmental collection of cell tower dump location information is becoming ubiquitous, in part because the Supreme Court in Carpenter v. United States declined to address whether it triggers Fourth Amendment protection. The Carpenter Court found that governmental acquisition of “seven days of [historical cell-site location information] constitutes a Fourth Amendment search.” But tower dumps are distinct from the Carpenter long-term historical CSLI in two main ways. First, cell tower dumps collect cell-site location information not from one person, but from hundreds or thousands of people. Second, because tower dump CSLI typically spans only several hours or even minutes, the amount of CSLI police acquire for any given individual captured in the tower dump is likely less than the 127 days of CSLI from one individual that law enforcement obtained in Carpenter.

Nonetheless, tower dumps still implicate massive amounts of user data and trigger privacy concerns  that potentially implicate the Fourth Amendment. Of the lower courts that have considered whether individuals have a reasonable expectation of privacy in cell tower dump CSLI, many have found that they do not. But most of those cases pre­dateCarpenter and do not account for its reasoning, and most post-Carpenter lower courts have not yet reached the merits of the issue.

As a result, this contribution seeks to guide future courts deciding whether to permit warrantless governmental acquisition of cell tower dump CSLI. Part I argues that cell tower dumps should constitute searches under the reasoning of Carpenterand Justice Alito’s concurrence in Jones because governmental acquisition from cell carriers of tower dump CSLI violates an individual’s reasonable expectation of privacy. Part II then proposes ways in which courts can minimize privacy intrusions into innocent individuals’ tower dump CSLI under either the Fourth Amendment  or the Stored Communications Act.

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