Update May 17, 2021: Since this post was published, the court unsealed its July 24, 2020 opinion denying the government's application for a geofence warrant.
Two federal magistrate judges in three separate opinions have ruled that a geofence warrant violates the Fourth Amendment’s probable cause and particularity requirements. Two of these rulings, from the federal district court in Chicago, were recently unsealed and provide a detailed constitutional analysis that closely aligns with arguments EFF and others have been making against geofence warrants for the last couple years.
Geofence warrants, also known as reverse location searches, are a relatively new investigative technique used by law enforcement to try to identify a suspect. 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 in a geographic area during a specific period of time in the past. The warrants therefore allow the government to examine the data from individuals wholly unconnected to any criminal activity and use their own discretion to try to pinpoint devices that might be connected to the crime. Earlier this summer, EFF filed an amicus brief in People v. Dawes, a case in San Francisco Superior Court, arguing that a geofence warrant used there violates deep-rooted Fourth Amendment law.
In Chicago, the government applied to a magistrate judge for a geofence warrant as part of an investigation into stolen pharmaceuticals. Warrant applications like these occur before there is a defendant in a case, so they are almost never adversarial (there’s no lawyer representing a defendant’s interest), and we rarely find out about them until well after the fact, which makes these unsealed opinions all the more interesting.
Here, the government submitted an application to compel Google to disclose unique device identifiers and location information for all devices within designated areas during forty-five minute periods on three different dates. The geofenced areas were in a densely populated city near busy streets with restaurants, commercial establishments, a medical office, and “at least one large residential complex, complete with a swimming pool, workout facilities, and other amenities associated with upscale urban living.”
As we’ve seen with other geofence warrants, the government’s original application proposed a three-step protocol to obtain the information. At the first step, Google would produce detailed and anonymized location data for devices that reported their location within the geofences for three forty-five minute periods. After that, the government would review that information and produce a list of devices for which it desired additional information. Then at the last step, Google would be required to produce information identifying the Google accounts for the requested devices.
On July 8, in the first unsealed opinion, U.S. Magistrate Judge M. David Weisman rejected the government’s request, finding “two obvious constitutional infirmities.” First, the court determined that the warrant was overbroad. While the court agreed that the government had established probable cause that a single cell phone user within the geofence might have commited a crime, the court held there was no probable cause to believe all the other devices in the area were connected to the crime as well. Importantly, the court rejected an argument we’ve seen the government make in the past that the search warrant was narrowly tailored because it covered only limited areas over short time periods. The court noted:
the geographic scope of [the] request in a congested urban area encompassing individuals’ residences, businesses, and healthcare providers is not ‘narrowly tailored’ when the vast majority of cellular telephones likely to be identified in this geofence will have nothing whatsoever to do with the offenses under investigation.
Second, the court determined that the warrant application failed to meet the Fourth Amendment’s particularity requirement. The court emphasized that there was nothing in the three-step protocol stopping the government from obtaining the user information for every device within the geofences.
In response to the court’s order, the government submitted an amended application by slightly narrowing the geographic scope of the geofences. A second magistrate judge, Judge Gabriel Fuentes rejected that application in an order that remains under seal.
Then, the government came back to the court yet again. This time, the government proposed eliminating the third step of the protocol. Judge Fuentes, however, was unmoved by the new changes because the government admitted it could just use a separate subpoena to get that detailed user information. In a 42-page decision rejecting the government’s application, Judge Fuentes, in large part, echoed Judge Wiesman’s earlier opinion. Notably, the court looked back to the Supreme Court’s decision in Ybarra v. Illinois (1979), a case that famously established that a warrant to search a bar and a bartender didn’t give police the power to search every person who happened to be in the bar. The court then rightly noted the similarities between the government’s unconstitutional conduct in Ybarra and the geofence warrant. It wrote that, similar to Ybarra, the government was seeking “unlimited discretion” to search all users’ devices in a given area—including users who merely walked along the sidewalk next to a business or lived in the residences above it—based on nothing more than their proximity to a suspected crime.
These decisions are good news. Judges too often rubber stamp warrant applications. But here, in careful, well-reasoned opinions that reflect what Judge Fuentes described as “[l]ongstanding Fourth Amendment principles of probable cause and particularity,” both judges stood up to protect constitutional rights in the face of government overreach.
Nonetheless, as the judges noted at various points in their opinions, geofence warrants are becoming more and more prevalent. Judge Weisman wrote at the end of his opinion:
[t]he government's undisciplined and overuse of this investigative technique in run-of the-mill cases that present no urgency or imminent danger poses concerns to our collective sense of privacy and trust in law enforcement officials.
Indeed, statistics from Google confirm that: “Year over year, Google has observed a 1,500% increase in the number of geofence requests it received in 2018 compared to 2017; and [as of December 2019], the rate  increased from over 500% from 2018 to 2019.” And news reports have revealed that prosecutors have used geofence warrants across the country. The risk of error and abuse with these warrants isn’t abstract. Last year, NBC News reported about an innocent person who got caught up in a geofence warrant.
That is deeply worrying. Indiscriminate searches like geofence warrants both put innocent people in the government’s crosshairs for no good reason and give law enforcement unlimited discretion that can be deployed arbitrarily and invidiously. But the Framers of the Constitution knew all too well about the dangers of overbroad warrants and they enacted the Fourth Amendment to outlaw them.