After BuzzFeed revealed late Sunday that a digital advertising firm, Titan 360 , was using public pay phones in New York City ( yes, they still exist ) to host Gimbal Bluetooth tracking beacons, the mayor’s office has now ordered them to come down.

The beacons can be used to log nearby phones’ Bluetooth addresses and mark the date, time, and location where they are seen. As such, the beacons can be used as a way to track physical movements of cellphone users, potentially allowing advertisers to serve those phones customized spots. (Users who have Bluetooth turned off on their phones will not be seen by the beacons.)

As recently as last month, Gimbal’s beacons—a rival to Apple’s iBeacon—were also being tested by another ad firm in GameStop stores in Texas. But in NYC, "the beacons will be removed over the coming days," according to New York City mayoral spokesman Phil Walzak, in a statement sent to Ars.

"While the beacons Titan installed in some of its phone[s] for testing purposes are incapable of receiving or collecting any personally identifiable information, we have asked Titan to remove them from their phones," he added. Walzak did not immediately respond to Ars’ further questions.

In a statement sent to Ars, Dave Etherington, Titan 360’s chief strategy officer, said that these beacons "do not collect user data/information, they do not send or push content, nor do they track people." Titan 360 did not respond to specific questions as to how the devices are used and if they are being used in other cities.

According to Titan 360, the company operates in "46 North American markets" including New York, Los Angeles, Chicago, Philadelphia, Boston, San Francisco, New Jersey, Dallas, Pittsburgh, Seattle, Minneapolis, and Charlotte.

"Beacons can only be utilized through users’ smartphones if, and only if, the user has downloaded a specific app with the technology imbedded and the user has specifically opted in," Etherington continued. "Titan is committed to testing new technologies which may have future benefits to its municipality partners and their constituents. At NYC’s request, Titan is in the process of removing the beacons from all NYC locations and ending the test."

If users downloaded the relevant app and enabled location tracking, Gimbal’s own privacy policy states that they may be subject to "periodic collection of your location (e.g., latitude/longitude coordinates) and time of day or your location when/if your device is near any of our Bluetooth beacons—small devices that may be placed, for example, in retail stores or other locations."