Just the Facts on 'Geofencing,' the Intrusive, App-Based 'Dragnet' That Sgt. Joe Friday Never Dreamed Of

As worshippers gathered at the Calvary Chapel in 2020, they were being watched from above.  

Satellites were locking in on cell phones owned by members of the nondenominational Protestant church in San Jose, Calif. Their location eventually worked its way to a private company, which then sold the information to the government of Santa Clara County. This data, along with observations from enforcement officers on the ground, was used to levy heavy fines against the church for violating COVID-19 restrictions regarding public gatherings.            

“Every Sunday,” Calvary’s assistant pastor, Carson Atherly, would later testify, the officers “would serve me a notice of violation during or after church service.”

Calvary is suing the county for its use of location data, a controversial tool increasingly deployed by governments at all levels – notably in relation to the U.S. Capitol riot on Jan. 6, 2021. While enabling law enforcement to more easily identify potential offenders, the practice, called “geofencing,” has also emerged as a cutting-edge privacy issue, raising constitutional issues involving warrantless searches and, with Calvary Chapel, religious liberty.

“We are in the space between the emergence of this technological practice and courts having ruled on its constitutionality,” said Alex Marthews, national chair for Restore the 4th, a nonprofit organization dedicated to the protection of the Fourth Amendment, which protects Americans’ rights against “unreasonable search and seizure.” 

“Geofencing” often begins with an innocent click. Smartphone apps ask if they can access location to improve service. When users say they yes, they often don’t realize that the apps that help them drive, cook, or pray are likely reselling their information to far-flung for-profit entities. This and other information detailing people’s behaviors and preferences is valuable for businesses trying to target customers. The global location intelligence market was estimated at $16 billion last year, according to Grand View Research, which predicts that figure will grow to $51 billion by 2030.

While it is legal for private companies to broker this information, constitutional questions arise when government accesses data from a third party that it would be prohibited from collecting on its own. The lawsuit filed by Calvary Chapel in August argues that Santa Clara County carried out a warrantless surveillance of the church when it acquired information in 2020 on the church’s foot traffic patterns collected by a research team from Stanford University. Court documents show the researchers acquired the information, which originated with Google Maps, from the location data company SafeGraph, which is also being sued by Calvary. 

Nicole Berger, SafeGraph’s senior vice president of operations, has said the Stanford team violated the company’s terms of service and non-commercial research agreement. For its part, Google has since cracked down on third-party vendors, though it still uses location and other data for its own operations.

Google was recently ordered to pay $93 million in a settlement over its collection of location data even after users turned off their location history. The company is also involved in an ongoing dispute in an Oakland, Calif., U.S. District Court over the company’s “Real Time Bidding” process, whereby customers’ personal information is auctioned off to advertisers, so that they can place targeted ads. According to the Calvary Chapel lawsuit, it was this process, among others, which enabled SafeGraph to collect users’ location data. 

Geofencing allows users to build a fence around certain areas or points-of-interest such as Calvary Chapel or the area near the Capitol on Jan. 6 and see when people entered that space.

It is becoming routine for law enforcement agencies to use warrants to require companies like Google to hand over location data that may be connected to criminal activity. Rep. Jim Jordan recently wrote a letter to Attorney General Merrick Garland saying, "The use of geofence warrants raises serious Constitutional concerns." Privacy advocates and a bipartisan group of legislators say that acquisition of such information without a warrant presents a troubling, and relatively new constitutional dilemma. The Calvary Chapel suit, as well as proposed legislation working its way through Congress, experts say, could prove important landmarks in resolving this tension between technological innovation and constitutional protections.

The Calvary Chapel suit stems from an earlier court case, in which the church was ordered to pay over $1 million in fines for violating county public health orders in 2020, by holding services on its premises without social distancing or masking. 

During the trial over the fines last year, it came to light that a research team headed by Stanford University professor of administrative law and statistical inference Daniel Ho had used SafeGraph data to provide Santa Clara County health officers with analysis on aggregate visits to Calvary Chapel covering the period of January 1, 2020, to February 28, 2021. In his 2022 “expert witness report,” Ho said the SafeGraph dataset he analyzed “was widely used during the pandemic to understand social distancing by public health authorities, including the Centers for Disease Control and Prevention, the California Governor’s Office, Los Angeles, San Francisco, San Jose, and Santa Clara County,” where information about “points-of-interest” included 1,576 religious organizations. 

Ho said he was able to estimate the average daily visits to the church.  

Data brokers, including SafeGraph, insist that their information is anonymized. But it is precisely the lack of specificity that worries its critics. “There's no particular individual who the government is suspicious of,” Adam Schwartz of the Electronic Frontier Foundation, told RealClearInvestigations. “It's a dragnet.”

Moreover, there is no guarantee that the data collected through geofencing stays anonymous. “It is often very easy to take supposedly de-identified data and re-identify a person,” said Schwartz, “And it's very, very easy to do that with location data.” The same phone spotted in two locations, he said, can be easily traced to a specific individual “because people have very unique travel and location patterns.”

At Calvary Chapel, for example, in-person surveillance conducted by the county, as well as numerous in-person depositions of Chapel members and employees during the previous legal contretemps between the county and the church that began in 2020, would have provided local officials with detailed knowledge of who was on the premises, and when.

The right to privacy, said Calvary Chapel attorney Mariah Gondiero, is “really going to be the key to this case,” with an overarching question of whether congregants have a reasonable expectation of privacy while in church. “You absolutely need a warrant,” she said, where that expectation exists.

In any event, critics say, law enforcement’s use of geofencing – even when it is backed by a warrant – violates the Fourth Amendment.

“There is very significant debate right now whether it is possible for a geofence warrant to meet the Fourth Amendment burden of particularity,” said Alex Marthews, referring to the legal principle that warrants must be specific to the individual, property, and place in order to be constitutional.

Geofencing proponents argue that it falls under the “administrative search” exception to the Fourth Amendment, which allows regulatory enforcement personnel to conduct warrantless searches in certain contexts where the greater good is at issue (i.e., police sobriety checkpoints, airport TSA scans).

In a written statement, a Santa Clara County public affairs spokesperson accused the Chapel of taking “out of context analysis of third-party, commercially available aggregate data that was used to respond to Calvary’s own allegations in a lawsuit that Calvary itself filed.”

In their complaint, Calvary Chapel attorneys assert that the county is arguing in effect “that, as long as they call it research, any level of government can target and spy on any individual or group at any time for any duration and, if they so choose, they can wield the collected data against said individuals or groups who oppose their orders.”

Marthews, who describes himself as someone who took “the threat of the peak of the current pandemic as having been a very serious one,” said government authorities at the time should nevertheless have recognized ‘the unique constitutional risks” that come with searching houses of worship and curtailing the free exercise of religion, “even in the context of a pandemic.” 

Public pushback is mounting against the sharing of location data. In a 2022 letter to Congress, numerous privacy and civil liberties groups petitioned for committee hearings on a bill called the Fourth Amendment is Not For Sale Act. The bill, which has a companion in the Senate that was introduced in 2021, would prohibit warrantless government purchases of cell phone location data from third party brokers. It passed unanimously through the House Judiciary Committee, 30-0, in July of this year, and awaits full review by the House. 

Last month, California passed a law calling for the creation of a mechanism that will allow consumers to demand that every data broker delete their personal information through a single request.

In the meantime, lawmakers, corporations, officials, and individual citizens are each grappling with the ethical problems presented by the coinciding twin novelties of COVID-19 and location data tracking. “Pandemic, the public good, the emergent nature of the [...] technological capabilities,” said Marthews, “is kind of a growing pain as we all kind of find our way through this technology and this pandemic together. I think that may be a fair assessment of this particular case.”

As for legislation, Schwartz describes himself as optimistic with regard to the eventual passage of the Fourth Amendment is Not for Sale Act. “I think there’s momentum,” he said. “It’s bipartisan.”