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Carpenter v. United States

In this amicus brief, the Brennan Center argues that historic data on the location of a cell phone reveals highly private information and that the government violated the Fourth Amendment by accessing it without a warrant.

Published: August 14, 2017

Carpenter v. United States involves the privacy of cell phone location information. Under current law, the government is not required to get a warrant for access to cell phone location data held by third-party service providers, following an antiquated rule known as the “third-party doctrine.” The Brennan Center believes this doctrine is a poor match for the digital age, and is urging the Supreme Court to hold that it does not apply to modern communications data.

The Brennan Center, in conjunction with the Electronic Frontier Foundation, Constitution Project, National Association of Criminal Defense Lawyers, and National Association of Federal Defenders, has filed a series of amicus briefs in Carpenter arguing that cell phone location data is private information, deserving of full Fourth Amendment protection. In 2016, the Sixth Circuit Court of Appeals reached the opposite conclusion, applying the third-party doctrine to hold that law enforcement does not need a warrant for data that is exposed to wireless carriers. (Read our Sixth Circuit brief here.) The Supreme Court has since agreed to hear the case, raising the possibility that the Justices will limit or overturn the doctrine to account for rapid changes in modern communications technology. (Read our brief in support of certiorari here.)

The Brennan Center’s latest Supreme Court brief explains what cell phone location data is, how it’s created, and how it can be stitched together to provide detailed information about an individual’s most private activities. The ubiquity and sophistication of modern cell phones has led to a surge in both availability and accuracy of location data. Service providers continue to install more cell phone towers, and users transmit data ever more frequently, automatically generating records that can identify an individual’s location with a level of precision that rivals GPS tracking. Service providers store the information for up to five years, creating an unprecedented opportunity for law enforcement to reconstruct past movements with remarkable accuracy.

Even in limited quantities, cell phone location information can be a telltale sign of private social, political, and religious activities protected by the Constitution. The Brennan Center argues that this data has such significant implications for freedom of speech and association that it demands a warrant supported by probable cause, no less than private papers in a desk drawer. The third-party doctrine predates the existence of cell phones and should not apply to the staggering amounts of personal data generated automatically, simply by carrying a cell phone.

Carpenter v. U.S. (Amicus Brief) by The Brennan Center for Justice on Scribd

USA v. Timothy Carpenter (Amicus Brief) by The Brennan Center for Justice on Scribd