Amster & Diehl on Against Geofences

Haley Amster (Stanford Law School) and Brett Diehl (Stanford Law School) have posted “Against Geofences” (Stanford Law Review, Forthcoming) on SSRN. Here is the abstract:

Since roughly 2016, law enforcement has increasingly relied on a new tool when investigating a crime with no suspects: geofence warrants. These warrants operate differently from a typical digital location history search warrant, through which law enforcement requires a third-party company to provide the location history of a particular user’s device. […] This Note aims to begin filling that analytical void by putting forward the first thorough scholarly analysis of the constitutionality of a geofence warrant.

This Note proceeds in five parts. Part I is a technology primer, explaining the steps involved in geofence warrants: the initial data dump, the expansion, and the unmasking. Part II catalogs the burgeoning geofence litigation, analyzing the first few federal magistrate opinions on the issue before briefly profiling other pending litigation. Part III looks more closely at the initial data dump, identifying the difficulty law enforcement has in meeting probable cause and particularity requirements due to the inherent breadth of the search. This Part explores potential constitutional limits on geofence warrants through analogies to the search of many people located at the scene of a crime, digital checkpoints, and area warrants. In this Part, the Note answers the question of whether probable cause must be shown for each device included in a digital search, exploring relevant scholarship regarding cell tower dumps. This Part then explores the difficulty in achieving constitutional tailoring, analogizing to digital searches of multi-occupancy buildings, and considers potential particularized search protocol that could indeed meet constitutional requirements. Part IV examines geofence warrants’ expansion and unmasking steps. It first argues that geofence warrants are unconstitutional general warrants because of the discretion given to law enforcement in the warrant execution. It then considers the additional steps as reaches beyond the scope of a warrant, or as multiple searches encompassed under one warrant.