US police agencies have been using a low-cost surveillance tool to track people’s phones

Fog Reveal uses phones' unique ad IDs to track users' movements.

Tim Robberts via Getty Images

Police and law enforcement agencies, even in small areas with fewer than 100,000 residents, have been using a low-cost phone tracking tool called Fog Reveal, according to AP and the EFF. AP has published a report detailing authorities' use of the tool since at least 2018 for various investigations, including to track murder suspects and potential participants in the January 6th Capitol riot. The tool, sold by Virginia company Fog Data Science LLC, doesn't need a warrant and can be accessed instantly. To get geofence data, authorities usually have to issue a warrant to companies like Google and Apple, and it could take weeks for them to get the information they need.

Fog Reveal, AP explains, uses advertising identification numbers, which are unique IDs assigned to each mobile device, to track people. It gets its information from aggregators that collect data from apps that serve targeted ads based on a user's location and interest, such as as Waze and Starbucks. Both the coffeehouse chain and the Google subsidiary denied explicitly giving their partners permission to share data with Fog Reveal.

The Electronic Frontier Foundation obtained access to documents about Fog through Freedom of Information Act requests, which it then shared with AP. EFF special adviser, Bennett Cyphers, describes the tool as "sort of a mass surveillance program on a budget." Its prices reportedly start at only $7,500 a year, and some agencies even share access with other nearby departments to bring costs down further. Looking at data from GovSpend, which monitors government spending, AP found that Fog managed to sell around 40 contracts to nearly two dozen agencies. Authorities have already used it to search hundreds of records from 250 million devices.

While Fog Reveal only tracks people using their advertising IDs that aren't connected with their names, authorities are able to use its data to establish "patterns-of-life" analyses. They can, for instance, establish that a specific ad ID belongs to a person who typically passes by a Starbucks from home on the way to work. Further, Fog gives authorities access to the movements of an ad ID going back to at least 180 days. Fog managing partner Matthew Broderick even recently admitted that the tool "has a three year reach back."

Authorities used the tool to varying degrees of success over the past years. Washington County prosecutor Kevin Metcalf said he has previously used Fog without a warrant for circumstances that required immediate action, such as to find missing children and to solve homicide cases. He said about privacy concerns surrounding Fog's use: "I think people are going to have to make a decision on whether we want all this free technology, we want all this free stuff, we want all the selfies. But we can't have that and at the same time say, 'I'm a private person, so you can't look at any of that."

The EFF, of course, doesn't share his sentiment. It called Fog "a powerfully invasive tool" and is encouraging people to disable ad ID tracking on their phones.