Geofence and Keyword Searches: Reverse Warrants and the Fourth Amendment

From thermal imaging and wiretaps to Global Positioning System (GPS) tracking and various forms of electronic eavesdropping, law enforcement’s use of emerging technologies is sometimes in tension with constitutional privacy protections. See, e.g., Kyllo v. United States, 533 U.S. 27, 29 (2001) (“This case presents the question whether the use of a thermal-imaging device aimed at a private home from a public street to detect relative amounts of heat within the home constitutes a search’ within the meaning of the Fourth Amendment.”); Olmstead v. United States, 277 U.S. 438, 455 (1928) (examining whether “evidence of private telephone conversations between the defendants and others, intercepted by means of wire tapping, amounted to a violation of the Fourth and Fifth Amendments”). Over the past century, federal courts have considered the extent to which the Fourth Amendment’s prohibition of unreasonable searches and seizures limits law enforcement’s use of such technologies. See, e.g., Kyllo, 533 U.S. at 2; Olmstead, 277 U.S. at 455. In 2026, the Supreme Court granted certiorari to consider the constitutionality of searches and warrants involving a relatively new, technology-assisted law enforcement tool—geofences. Chatrie v. United States, No. 25-112, 2026 WL 120676 (U.S. Jan. 16, 2026). Some state courts have opined on the constitutionality of similar investigatory tools, including those known as keyword warrants. E.g., People v. Seymour, 536 P.3d 1260 (Colo. 2023). Both geofence and keyword warrants are sometimes described as reverse warrants. Using a reverse warrant, law enforcement essentially works backwards from the traditional process of identifying a known suspect and then obtaining a search warrant to gather information on that suspect. Instead, with a reverse warrant, law enforcement first identifies facts that may constitute incriminating evidence, such as the time and location of a crime or an internet search for an address where a crime occurred. Law enforcement then attempts to identify a suspect by compelling user information correlating to those facts from a technology provider. See, e.g., id. at 1268 (describing how and why law enforcement obtained keyword warrant); see also United States v. Smith, 110 F.4th 817, 826 (5th Cir. 2024), cert. denied, 146 S. Ct. 356 (2025) (describing law enforcement use of geofence warrant in particular case). The use of reverse warrants, particularly geofence warrants, has garnered media attention and legislative interest at the state and federal levels. In 2023, Google announced that it would reduce the default length of time it stores the location information typically sought by geofence warrants. It also announced that it would migrate user data from internal servers to users’ individual devices, which could effectively make it impossible for Google to share user location data with law enforcement. The move drew interest from some observers who believe it could significantly curtail the use of geofence warrants, although at least one federal appellate court has observed that, as of 2024, the government was still seeking geofence data from Google. Smith, 110 F.4th at 822 n.3. Law enforcement may also continue to seek geofence data or other information covered in this report from other companies. This report examines evolving legal issues regarding reverse warrants. It summarizes Fourth Amendment principles and the caselaw surrounding reverse warrants. The report concludes with considerations for Congress.