Phone booths are well on their way to becoming obsolete. In London, disused ones are being converted into mobile phone charging stations. In New York, there are murmurings that some may become WiFi hotspots.

Unbeknownst to New Yorkers, however, an advertising company has already found another use for phone booths: installing “beacons”, which enable them to track smartphones as they move around the city.

Beacons are small devices that emit Bluetooth signals which smartphones can read. They can alert customers to sales or offers; they’ve also been used at festivals and stadiums to tell visitors which entrances are least crowded. Most also track the phone’s location, in order to, for example, send a notification about a sale when a user approaches a particular shop.

Users must “opt-in” to allow notifications or location tracking through particular apps. The problem is, once beacons are enabled on one app, they’re enabled on the smartphone as a whole.

So users may have enabled a beacon app for a football game, without realising that beacons all over New York can now access their location. The only way to permanently disable the technology is to delete all apps with the beacon function enabled.

Buzzfeed broke the story on Monday, by using an app that lists nearby beacons to detect the bugged phone booths. It found that Titan, the company responsible for the phone booths, had installed the beacons with city authorities’ permission, but with no public consultation. To quote the story:

New York City residents had no say in the deployment of Titan’s beacons. Titan notified the Department of Information Technology & Communications of its plans to install the beacons in 2013, which the city agreed to without a formal approval process because, according to Sbordone, the company said it was using the devices for maintenance purposes only.

Titan installed the beacons from September to November 2013; a source with knowledge of the situation alerted BuzzFeed News to the program anonymously for fear, the source said, of being fired for speaking publicly.

Titan doesn’t seem to have used information taken from phones for any commercial purposes. But the beacons, manufactured by Gimbal, operate through “sightings” – interactions with phones communicated to a central server – implying that they did indeed collect location information without warning or permission. Now, the mayor’s office has asked Titan to remove them.

The affair has raised issues about how the beacons should be used in public spaces. Doug Thompson, CEO of a beacon technology company, told Buzzfeed that customers should be warned when they enter zones containing beacons.

Half of the top 100 retailers in the US are currently looking into using beacons for marketing, so it looks like this isn’t the last we’ll be hearing of the issue.