Ever hear of a “geofence search warrant” (AKA; Reverse Location Warrant)?  I had not, at least until recently turned onto the subject by a concerned investigator. A geofence (or “geo-fence”) warrant is a search warrant issued by a court allowing law enforcement to search a database to find all active mobile devices within a particular geofence (or geographical) area during a specified period of time. Such warrants are a relatively new (although increasingly popular) investigative technique used by law enforcement in its attempt to identify a specific suspect in a crime (or, more often, series of crimes) under investigation.  Geofence warrants are used to obtain information from databases (such as Google’s “Sensorvault”) where a user’s historical geo-location data is stored.   Unlike ordinary warrants for electronic records that identify the suspect in advance of the search, geofence warrants essentially work backwards by scooping up the location data from every device that happened to be within a specifically identified geographical area during a specific period of time in the past. The warrants therefore necessarily allow the government to examine the data from a wide range of individuals wholly unconnected to any criminal activity, with law enforcement agents using their own “unbridled” discretion in attempting to pinpoint a specific device or devices that might be connected to the crime under investigation. Geofence warrants have led to privacy and Fourth Amendment concerns where innocent passersby have been subjected to unjustified searches of their Google accounts just by being at a particular location near an active crime scene.  This is how geofence warrants work:  The government’s application for a geofence warrant typically involves a three-step protocol to obtain the information. At the first step, Google, in response to a warrant, produces detailed and “anonymized” (i.e., “having had identifying particulars or details removed”) location data for devices that reported their location within the geofence (i.e., a specific geographical area) within one or more specific time periods during which a crime or crimes occurred. Upon receiving the requested information, law enforcement agents then review those records and, at their own discretion, narrow them down to a list of devices for which they desire additional information. The last step is Google being required to produce information identifying the Google accounts for the selected devices.  In the process, the Google records of many innocent individuals are necessarily subjected to law enforcement scrutiny. There are no reported appellate court decisions on the constitutionality of geofence warrants in either California, the Ninth Circuit, or the U.S. Supreme Court. However, three lower level federal trial courts, all out of the Seventh Circuit (Illinois), have issued memorandum opinions in response to warrant applications.  Two of those opinions explain why applications for such a warrant were denied, noting several constitutional infirmities in their use.  (See (1) In re Search of Info. Stored at Premises Controlled by Google (7th Cir. U.S. Dist. Ct., Nor. Dist., East. Div., of Ill., Aug. 24, 2020) 2020 U.S.Dist. LEXIS 152712, and (2) In re Search of Info. Stored at Premises Controlled by Google (7th Cir. U.S. Dist. Ct., Nor. Dist. of Ill., July 8, 2020) 2020 U.S.Dist. LEXIS 165185.)  A third opinion (see In re Search Warrant Application for Geofence Location Data Stored at Google Concerning an Arson Investigation (7th Cir. U.S. Dist. Ct., Nor. Dist., East. Div., of Ill., Oct. 29, 2020) 2020 U.S. Dist. LEXIS 201248.) granted the agents’ application for a search warrant, describing how this particular petition (the warrant itself remaining sealed) differs from the two previous denials.  In the two denials, the federal district court magistrates rejected the government’s applications for geofence warrants, ruling that the Government’s attempts to obtain such a warrant violates Fourth Amendment constitutional restrictions on “overbreadth” as well as the requirement that warrants describe the items to be seized “with particularity.”  In the third search warrant application, however, the federal magistrate granted the Government’s request, going to great lengths in discussing how the agents were able to minimize the constitutional issues by limiting their warrant application in the time spans described (from between 15 to 37 minutes, respectively).  They also minimized the geographical locations for which Google’s data was to be concerned, typically to a specific roadway or commercial parking lot.  As described by the magistrate, the agents “narrowly crafted (the time spans and locations) to ensure that location data, with a fair probability, will capture evidence of the crime only.” In writing the warrant application in such a manner, the magistrate noted that the agents limited the warrant request in its scope as much as possible, thus minimizing the constitutional issues.  I have the full written decisions (plus a news article summarizing the issue) which I will pass onto you upon request.  None of these cases, however, are controlling authority on these issues for what we do in California (state or federal).  But the Illinois magistrates’ reasoning in each case (being the only published decisions on this issue) cannot be ignored, and will likely be considered when your case—if you’re using geofence warrants—is challenged in court.  So just be forewarned.