Aug 27, 2021 6:19 PM

An Explosion in Geofence Warrants Threatens Privacy Across the US

New figures from Google show a tenfold increase in the requests from law enforcement, which target anyone who happened to be in a given location at a specified time.

Police around the country have drastically increased their use of geofence warrants, a widely criticized investigative technique that collects data from any user's device that was in a specified area within a certain time range, according to new figures shared by Google. Law enforcement has served geofence warrants to Google since 2016, but the company has detailed for the first time exactly how many it receives.

The report shows that requests have spiked dramatically in the past three years, rising as much as tenfold in some states. In California, law enforcement made 1,909 requests in 2020, compared to 209 in 2018. Similarly, geofence warrants in Florida leaped from 81 requests in 2018 to more than 800 last year. In Ohio, requests rose from seven to 400 in that same time.

Across all 50 states, geofence requests to Google increased from 941 in 2018 to 11,033 in 2020 and now make up more than 25 percent of all data requests the company receives from law enforcement.

A single geofence request could include data from hundreds of bystanders. In 2019, a single warrant in connection with an arson resulted in nearly 1,500 device identifiers being sent to the Bureau of Alcohol, Tobacco, Firearms, and Explosives. Dozens of civil liberties groups and privacy advocates have called for banning the technique, arguing it violates Fourth Amendment protections against unreasonable searches, particularly for protesters. Now, Google’s transparency report has revealed the scale at which people nationwide may have faced the same violation.

“There’s always collateral damage,” says Jake Laperruque, senior policy counsel for the Constitution Project at the nonprofit Project on Government Oversight. Because of their inherently wide scope, geofence warrants can give police access to location data from people who have no connection to criminal activities.

"We vigorously protect the privacy of our users while supporting the important work of law enforcement,” Google said in a statement to WIRED. “We developed a process specifically for these requests that is designed to honor our legal obligations while narrowing the scope of data disclosed."

Just this week, Forbes revealed that Google granted police in Kenosha, Wisconsin, access to user data from bystanders who were near a library and a museum that was set on fire last August, during the protests that followed the murder of George Floyd. Google handed over the “GPS coordinates and data, device data, device IDs,” and time stamps for anyone at the library for a period of two hours; at the museum, for 25 minutes. Similarly, Minneapolis police requested Google user data from anyone “within the geographical region” of a suspected burglary at an AutoZone store last year, two days after protests began.

Laperruque argues that geofence warrants could have a “chilling effect,” as people forgo their right to protest because they fear being targeted by surveillance. Just this week, Kenosha lawmakers debated a bill that would make attending a “riot” a felony. Critics noted that such a bill could penalize anyone attending peaceful demonstrations that, because of someone else’s actions, become violent. Similarly, geofence data could be used as evidence of guilt not just by being loosely associated with someone else in a crowd but by simply being there in the first place.

Geofence warrants work differently from typical search warrants. Usually, officers identify a suspect or person of interest, then obtain a warrant from a judge to search the person’s home or belongings.

With geofence warrants, police start with the time and location that a suspected crime took place, then request data from Google for the devices surrounding that location at that time, usually within a one- to two-hour window. If Google complies, it will supply a list of anonymized data about the devices in the area: GPS coordinates, the time stamps of when they were in the area, and an anonymized identifier, known as a reverse location obfuscation identifier, or RLOI.

While this initial list may include dozens of devices, police then use their own investigative tools to narrow the list of potential suspects or witnesses using video footage or witness statements. Google provides the more specific information—like an email address or the name of the account holder—for the users on the narrower list.

Laperruque proposes, at minimum, that law enforcement should be pushed to minimize search areas, delete any data they access as soon as possible, and provide much more robust justifications for their use of the technique, similar to the requirements for when police request use of a wiretap.

“Why is this size of area necessary? Why this time? Why wouldn't a more narrow setting work? Why wouldn't just one individual’s phone work?” he says. “It should be a last resort, because it’s so invasive.”

The fact that geofence results indicate only proximity to a crime, not whether someone broke the law or is even suspected of wrongdoing, has also alarmed legal scholars, who worry it could enable government searches of people without real justification.

Geofence warrants aren’t only issued to Google. Apple, Uber, and Snapchat have all received similar requests from law enforcement agencies. Each of these companies regularly share transparency reports detailing how often they hand over user info to law enforcement, but Google is the first to separately detail geofence warrants.

Last year, advocates from the New York Civil Liberties Union, the Surveillance Technology Oversight Project, and a host of other organizations began working with New York state senator Zellnor Myrie and assemblymember Dan Quart to pass the "reverse location and reverse keyword search prohibition act," the nation’s first proposed ban on geofence warrants. The bill would also ban “keyword searches,” a similarly criticized investigative tactic in which Google hands over data based on what someone searched for. Speaking to WIRED last year, Quart called the tools a “fishing expedition that violates people's basic constitutional rights.”

But regulation can only move so fast. The New York bill is still far from passage and impacts just one state. Meanwhile, places like California and Florida have seen tenfold increases in geofence warrant requests in a short time. Transparency is important in understanding the scale of the risks to privacy, but there are still no clear ways to limit the use of these tools nationwide. In the meantime, as law enforcement relies on the warrants, countless more passersby will become “collateral damage.”