In an amicus brief filed in the U.S. Supreme Court, leading technology experts represented by the Knight First Amendment Institute at Columbia University argue that the Fourth Amendment should be understood to prohibit the government from accessing location data tracked by cell phone providers — “cell site location information” — without a warrant.

“The government’s surveillance powers have outpaced constitutional protections meant to prevent overreach and abuse,” said Alex Abdo, senior staff attorney at the Knight Institute. “Government agents shouldn’t be able to track a person’s movements for weeks or months without first obtaining a warrant from a judge.”

"Government agents shouldn’t be able to track a person’s movements for weeks or months without first obtaining a warrant from a judge."  

Law enforcement agencies are increasingly requesting cell site location information from service providers, with AT&T receiving close to 60,000 requests in 2015 alone. Officials are obtaining this data without first obtaining warrants, and without broad public awareness that cell phone providers even possess it. Nearly three-quarters of cell phone users report being within five feet of their phones most of the time, and cell phone providers commonly record time-stamped location data with an accuracy rivaling that of GPS systems. This data is extraordinarily rich and can be used, for example, to determine whether someone has been present at an Alcoholics Anonymous meeting, an abortion clinic, or the office of an attorney who represents government whistleblowers. It can also be used to “fingerprint” individuals based on their patterns of movement and, when combined with other location data, to infer friendships and associations.

"In today’s digital age, our phones can reveal more about us than could be discovered from a search of our private homes," said Ashkan Soltani, an independent researcher and former chief technology officer of the Federal Trade Commission. “Nearly all our interactions—communicating with family and friends, navigating to work or childcare, purchasing goods—involve collection of our data. The outcome of this case could dictate what digital privacy protections, if any, we can reasonably expect to have over our information in the future.”

In the brief, the technologists explain that cell site location information is likely to become increasingly precise. At the same time, cell site location information is becoming easier and cheaper for law enforcement to store, obtain, and analyze. Allowing government agents warrantless access to this sensitive information threatens privacy and the freedoms of speech and association, heightening the need for constitutional safeguards. The brief urges the Supreme Court to prohibit the government from obtaining cell site location information without first obtaining a warrant.

The brief was filed yesterday in the case Carpenter v. United States on behalf of Ashkan Soltani, Dr. Edward W. Felten, Dr. Matt Blaze, Dr. Steven M. Bellovin, Bruce Schneier, Dr. Joseph Lorenzo Hall, Morgan Marquis-Boire, Dr. Nicholas Weaver, Dr. Stephen Checkoway, Dr. Dan S. Wallach, Adam Shostack, Dr. Rebecca Wright, Dr. Carrie E. Gates, Scott Bradner, Dr. Susan Landau, Dr. Ben Adida, Dr. Nadia Heninger, Philip Zimmermann, and Dr. Sharon Goldberg. The brief was drafted by Brian Willen, Jack Mellyn, and Samuel Dippo of Wilson Sonsini Goodrich & Rosati, and by the Knight Institute.

Read the amicus brief.

About the Knight Institute

The Knight First Amendment Institute is a non-partisan, not-for-profit organization established by Columbia University and the John S. and James L. Knight Foundation to defend the freedoms of speech and press in the digital age through strategic litigation, research, and public education.