Against Geofences

61 Pages Posted: 28 Apr 2021 Last revised: 28 Mar 2022

See all articles by Haley Amster

Haley Amster

Stanford Law School

Brett Diehl

Federal Defenders of San Diego, Inc.; Stanford Law School

Date Written: April 16, 2021


Law enforcement is increasingly relying on a new tool when investigating crimes with no suspects: geofence warrants. Geofence warrants take advantage of geofence technology, which constructs a virtually bounded geographic area and identifies all users present within that area during a given time window. Google, the primary recipient of geofence warrants, has adopted a policy of objecting to any geofence request that is not a probable-cause warrant. So far, law enforcement has complied. This has caused courts and litigators to defer the question of whether, under Carpenter v. United States, a probable-cause warrant is necessary. Instead, these parties have located the legality of geofence warrants in less explored regions of the Fourth Amendment as applied to new technologies: probable-cause and particularity requirements, the few exceptions to those requirements, and the proper execution of a warrant.

This Note fills an analytical void by providing a comprehensive examination of these less explored regions. The Note first provides a technology primer, detailing the three steps involved in geofence warrants: the initial data dump, selective expansion, and unmasking. It then provides background on relevant Fourth Amendment law, explaining why the familiar “reasonable expectation of privacy” test has not yet proven dispositive in geofence-warrant litigation. After cataloguing burgeoning geofence litigation, the Note examines the initial data dump, identifying the difficulty of meeting probable-cause and particularity requirements due to the inherent breadth of the search. Here the Note answers the question of whether probable cause must be shown for each device included in a digital search, based in part on jurisprudence regarding checkpoints, area warrants, and searches of many people in a commercial location. The Note next examines the selective expansion and unmasking steps, arguing (1) that geofence warrants are unconstitutional general warrants because of the discretion given to law-enforcement officials in warrant execution; and (2) that these steps may impermissibly increase a warrant’s scope or constitute multiple searches under one warrant. The Note concludes by considering the broader implications of corporate policy shaping Fourth Amendment guardrails.

Suggested Citation

Amster, Haley and Diehl, Brett and Diehl, Brett, Against Geofences (April 16, 2021). Stanford Law Review Volume 74, p. 385, Available at SSRN:

Haley Amster (Contact Author)

Stanford Law School ( email )

559 Nathan Abbott Way
Stanford, CA 94305
United States

Brett Diehl

Stanford Law School ( email )

559 Nathan Abbott Way
Stanford, CA 94305
United States

Federal Defenders of San Diego, Inc. ( email )

225 Broadway
Ste. 900
San Diego, CA 92101
United States

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