Courts are struggling to apply the Fourth Amendment’s particularity requirement to new surveillance warrants that compel technology companies to search users’ aggregated location and activity data.
Courts are struggling to apply the Fourth Amendment’s particularity requirement to new surveillance warrants that compel technology companies to search users’ aggregated location and activity data.
The Digital Dragnet: Warrants on Aggregated Data
Cell phones are ubiquitous in the modern age. From location history stored by Google to search terms logged by providers, digital data is constantly proliferating, supplying law enforcement with unprecedented investigation tools. However, the use of these tools—specifically geofence warrants and reverse keyword warrants—has caused a direct conflict between investigative techniques and a core constitutional protection. Unlike traditional warrants, geofence and reverse keyword warrants, or reverse warrants, compel technology companies to search databases to identify individuals in a digital or physical space at a specific time.
The fundamental question for courts to consider is whether these digital dragnets satisfy the Fourth Amendment’s requirements of Probable Cause and Particularity, or if they are a modern iteration of the unconstitutional general warrants the framers sought to prohibit. Courts are struggling to adapt Fourth Amendment precedent to the mechanisms of these modern warrants, as shown by the jurisprudential split between the Fourth and Fifth Circuits.
The Mechanisms of Digital Surveillance
These new investigative tools are in common use and demonstrate a shift away from traditional police procedure. Since their introduction, they have become one of law enforcement’s favorite investigative tools. Rather than identifying a person and searching their property, geofence warrants identify a location or a digital activity and then search for the person associated with it. The fundamental characteristic of reverse warrants is their retrospective operation: they begin with a completed crime and work backward through vast amounts of digital data to identify a suspect. This process compels private companies to spearhead a massive data search.
Reverse warrants are typically used by law enforcement in scenarios where traditional investigative methods fail to identify a suspect. A common scenario is where a serious crime occurs and the investigation determines the approximate time and location of the event but cannot identify any suspects. Reverse warrants are then used to generate a preliminary list of potential suspects that fit particular characteristics from a broad pool of individuals. This reliance on searching broad data sets to develop individualized suspicion is what makes reverse warrants controversial.
Types of Reverse Warrants
There are two types of reverse warrants in wide use today: Geofence warrants and Reverse Keyword Warrants. Geofence warrants request data from a technology company for all devices that were physically present within a defined geographical area—the geofence—during a certain time frame. The typical process involves multiple steps that involve significant coordination between the government and tech companies.
First, the government seeks anonymized, time-stamped location coordinates for every device in the area. The government then reviews the list, and uses other investigatory techniques to narrow it down, sometimes requesting more information. Ultimately, the government requests identifying information like usernames, birthdays, and information about the target users’ phones.
The goal of requesting only anonymized information initially is to narrow down the search before revealing any identifying details. This is necessary because the law enforcement agency does not have any prior individualized suspicion. The effectiveness of these warrants becomes clear when leads are generated where none existed before, but their breadth has become a source of legal controversy.
Reverse keyword warrants operate similarly to geofence warrants; however, the target of these warrants is not a physical location, but the knowledge or intent of the user. Reverse keyword warrants compel search engine providers to disclose the identities of users who searched for specific terms or phrases. The warrants further compel tech companies to comb through users’ search history to provide law enforcement with a suspect list based on relevant search terms within a relevant jurisdiction or time period. Reverse keyword warrants function similarly to geofence warrants, starting with a broad search of activity and winnowing down to specific digital identities. Because search history is capable of revealing intimate details of one’s life, the source of controversy around these warrants is the government’s ability to use expressions of a person’s thoughts as a basis for suspicion.
The Fourth Amendment Requirements of Probable Cause and Particularity
The text of the Fourth Amendment clearly states the requirements of a warrant, including probable cause and particularity:
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
Critics of geofence and reverse keyword warrants claim that they do not hold up to the constitutional standards of probable cause and particularity. Proponents, on the other hand, claim that these reverse warrants pass Constitutional muster.
Probable Cause
Probable cause is a legal standard that law enforcement must meet to obtain a warrant. Defined in Illinois v. Gates, probable cause exists when there is a fair probability that evidence of a crime will be found in a particular place. Critics of reverse warrants point out, as a threshold issue, that these warrants do not identify a particular suspect for the crime because no suspect yet exists. It is argued that reverse warrants actually seek facts that would create probable cause to identify a suspect, which does not equate to actually having probable cause for a search of the user. Further, it is argued that the warrants rest on an assumption that users in a particular area or who search certain words could be guilty of a crime. Critics argue these assumptions are insufficient for a finding of probable cause.
Proponents, however, argue that probable cause is a flexible standard, sufficiently met in the context of a reverse warrant. Supporters assert that probable cause exists under Gates because police have reason to believe that evidence—the identity of the perpetrator—will be found somewhere within the vast data set being requested. Therefore, probable cause exists because police have a fair probability that a search of the company’s servers will yield necessary evidence. For geofence warrants, this means probable cause is found in the certainty that evidence will be found on the servers of the company receiving the request.
Particularity
The founders understood that a particularity requirement for warrants would combat the evils of historical writs of assistance, which were general warrants used to raid homes and perpetrate unreasonable searches and seizures. The requirement aims to ensure that the warrant is tailored to its justifications. The Fourth Amendment stipulates that a warrant must “particularly describe the place to be searched, and the persons or things to be seized,” prohibiting general searches.
One of the most potent arguments against reverse warrants is that they are the modern equivalent of general warrants, used to search broadly and without specific targets. Critics contend reverse warrants fail the particularity requirement because they compel the search of data belonging to thousands of innocent people simply because they were at the wrong place at the wrong time. They argue that a warrant must instead link the crime to a specific person or place at the time it is issued. The reverse warrant, effectively, is a request to produce a massive digital haystack.
Proponents counter that reverse warrants can be sufficiently particular so long as they are not overly broad. Ideally, the warrants specify the precise geographic coordinates, time frame, and data type to remain within constitutional bounds. The multi-step process used to narrow the data also acts as a necessary restriction on the capture of data to minimize law enforcement discretion in the execution of a warrant. A proposed method of executing reverse warrants in conformance with particularity principles suggests that law enforcement draw multiple relevant geofence boundaries and then search for users found in all boundaries.
The Split in Judicial Authority
This entire legal area is scrutinized under the shadow of the Supreme Court’s landmark ruling in Carpenter v. United States. In Carpenter, the Court addressed whether the government conducting a warrantless search of a person’s historical cell-site information (CSLI) violated the Fourth Amendment. The Court ruled that it did, establishing that a person has a reasonable expectation of privacy in their CSLI due to its comprehensive and aggregated nature. The Court held that the acquisition of such vast, aggregated location data was considered a search under the Fourth Amendment, and therefore, was subject to its warrant standards.
Courts that oppose the use of reverse warrants, such as the Fifth Circuit, view these warrants and their searches as a logical extension of the unconstitutional surveillance in Carpenter. These courts argue that geofence warrants are an even more invasive form of the intrusion that the Carpenter majority focused on because they capture the location history of thousands of non-suspects. Conversely, courts that uphold reverse warrants attempt to distinguish them from Carpenter based on the defendant’s voluntary act of sharing data with the technology provider. They argue that a reverse warrant for a small area and brief period of time does not constitute the same kind of “detailed chronicle” of an individual’s life.
The constitutional ambiguities surrounding reverse warrants have led to a patchwork of various rulings across federal and state courts. The Supreme Court of the United States has yet to provide guidance on reverse warrants, and the admissibility of the evidence these warrants produce hinges on a split in judicial authority.
The Fifth Circuit’s Take
The Fifth Circuit Court of Appeals forcefully rejected the use of geofence warrants in United States v. Smith. In Smith, the court deemed geofence warrants to be “general warrants categorically prohibited by the Fourth Amendment” and ruled them unconstitutional. The Fifth Circuit heavily focused on the fact that the warrant compelled a search for vast amounts of data belonging to non-suspects in coming to its conclusion. The court stated that the “quintessential problem” with geofence warrants is they do not identify a specific user for the search, but only a boundary where any user may appear. Ultimately, the Fifth Circuit ruled that the warrant was unconstitutional because it allows the same type of rummaging as a general warrant, which the Fourth Amendment was designed to prevent.
The Fourth Circuit’s Take
Sharply contrasting the Fifth Circuit, the Fourth Circuit affirmed the constitutionality of reverse warrants in United States v. Chatrie. In Chatrie, the defendant was convicted of bank robbery using evidence obtained from a geofence warrant. In its opinion, the Fourt Circuit addressed a more fundamental question of whether the government’s access to such data constitutes a Fourth Amendment “search” in the first place. The court held that the government’s conduct did not constitute a search because Chatrie lacked a reasonable expectation of privacy in the limited data collected. Crucially, the court differentiated the data in Chatrie from the data at issue in Carpenter. It distinguished the data used in reverse warrant from CLSI date by pointing out the fact that Google’s location setting is turned off by default and only enabled by the user’s affirmative act, meaning the data is voluntarily shared and therefore not subject to Fourth Amendment protection.
Looking Ahead: The Supreme Court and Chatrie
Following the Fourth Circuit’s decision, Okello Chatrie petitioned the Supreme Court of the United States to resolve the constitutional issue. On January 16, 2026, the Supreme Court granted certiorari in Chatrie v. United States, marking the first time the Supreme Court has agreed to directly address the constitutionality of geofence warrants. The Court granted its review on a single fundamental question—whether the execution of the geofence warrant violated the Fourth Amendment—signaling its intent to provide a definitive ruling on the scope of digital privacy in the age of aggregated data.
The case has drawn vast amounts of attention from civil liberties groups, technology giants, and legal scholars, with over 30 amicus curiae briefs filed. The Supreme Court is scheduled to hear oral arguments on April 27, 2026. All of this suggests that the Court’s decision in Chatrie will likely be the most significant Fourth Amendment ruling since Carpenter. The decision will determine whether one of law enforcement’s favorite investigative approaches is a permissible tool or a violation of the foundational right to be secure against unreasonable searches.
Conclusion
This conflict over reverse warrants represents a critical legal juncture where the ubiquitous nature of digital data confronts the foundational protections of the Fourth Amendment. Geofence and reverse keyword warrants have generated profound constitutional dispute amongst legal scholars and practitioners alike. The Fifth Circuit’s rejection of geofence warrants is based on particularity grounds, while the Fourth Circuit’s upholding of a similar warrant denies that a Fourth Amendment “search” occurred. This diversion on the application of existing precedent, particularly the Carpenter ruling, highlights a need for definitive guidance from the Supreme Court of the United States, as admissibility of digital evidence currently hinges on geography. With the Supreme Court’s recent grant of certiorari in Chatrie v. United States, the Court is now poised to decide whether reverse warrants can coexist with the Fourth Amendment. Absent a clear constitutional mandate, the legal status of reverse warrants remains uncertain. The resolution of the conflict will ultimately define the scope of the Fourth Amendment in the modern, digital age.
