United States v. Carpenter

Brief of Amici Curiae American Civil Liberties Union Foundation, American Civil Liberties Union Foundation of Michigan, Brennan Center for Justice, Center for Democracy & Technology, Electronic Frontier Foundation & National Association of Criminal Defense Lawyers in Support of Defendants-Appellants’ Seeking Reversal.

Brief filed: 03/09/2015


United States v. Carpenter

6th Circuit Court of Appeals; Case No. 14-1572 & 14-1805

Prior Decision

Case below No. Crim. 12-20218 (E.D. Mich.).


Warrantless acquisition of long-term historical cell site location information violated defendants’ reasonable expectation of privacy under the Fourth Amendment. Defendants’ cell site location information obtained by the government reveals invasive and accurate information about their location and movements over time. Obtaining 127 or 88 days’ worth of cell phone location data is a “search” under the Fourth Amendment requiring a warrant based upon probable cause. Cell phone providers’ ability to access customers’ location data does not eliminate cell phone users’ reasonable expectation of privacy in that data. Even if the good faith exception applies, this court should decide the Fourth Amendment question.

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Nathan Freed Wessler and Ben Wizner, American Civil Liberties Union Foundation, New York, New York; Kristina W. Supler, MCarthy, Lebit, Crystal & Liffman Co. L.P.A., Cleveland, OH.