A report from BuzzFeed News Wednesday suggests that the tracking beacons that cropped up in New York phone booths last year have spread to new cities, including Los Angeles and Chicago. The beacons have been sprinkled around transit centers, including Chicago Transit Authority rail stops and LA bus stops.

The beacons, created by Gimbal, connect with devices like smartphones via Bluetooth and can harvest information like the device's Bluetooth address, as well as the date, time, and location of connection. The beacons in New York were installed as a "test" by advertising company Titan 360. Though officials called for their removal over a year ago, they were not taken out of phone booths until earlier this month, after they were used in promotions for the Tribeca Film Festival and shopping app ShopAdvisor.

Marketing company Martin Outdoor Media confirmed the beacons' existence in LA to BuzzFeed News, as did the CTA in Chicago. Martin called the beacons part of a "pilot program" in a press release last week, while the CTA stated its beacons were part of a "two-week test," to be followed up by a bigger test for a longer period with beacons placed and tracked by Titan.

Used as a network, beacons can track the presence and movement of individual people. Individually, the beacons are installed in outdoor ads and can act as a rough indicator of how many people are seeing a certain ad and what combination of ads they see through their movement patterns. BuzzFeed also reported an anonymous tip that the Gimbal beacons were also placed around San Francisco, though the outlet was unable to confirm that information. Titan did not immediately respond to a request for comment.