New York City quickly announced it would get rid of devices that could turn phone booths into cellphone trackers after the program was revealed this morning.

A Buzzfeed investigation published today found that the city allowed 500 radio transmitters, called “beacons,” to be installed in pay phone booths, apparently thickly concentrated in lower and mid-Manhattan. A few hours later, the Mayor’s office said they would have them removed.

Though they could be woven into a location-aware advertising network, the beacons are there for maintenance notifications only and are not yet being used for commercial purposes, according to Titan, the firm that runs the advertising displays for thousands of city phone booths. There was no public announcement when the devices were installed.

Titan uses beacons made by a company called Gimbal, which connect with phones and have the ability to send notifications – for instance, a store might use them to alert customers to discounts – and to collect data.

In order for a Gimbal beacon to pick it up, a smartphone must have Bluetooth enabled, and must also have a third-party app that uses Bluetooth beacon technology, referred to variously as “Bluetooth Low Energy,” “Bluetooth LE,” or “iBeacon.” The owner would, in theory at least, have also had to “opt-in” to the service when installing said app — although such permission might just look like the familiar, innocuous-sounding “[This app] would like to send you notifications,” which was the prompt presented to Forbes’ Kashmir Hill when installing a Gimbal-friendly app from the Tribeca Film Festival.

If you do connect to its Bluetooth beacons, Gimbal is supposed to anonymize your information before sending it to customers — no name or email address — but it can still see when and where you passed a beacon. In some cases, Buzzfeed reported, Gimbal can “collect data about the websites you visit, the apps on your phone, and the ‘frequency and duration of app usage,’” and develop profiles of users, guessing at your age, gender, ethnicity, income, interests, and where you spend your time.

Titan confirmed to Buzzfeed that it had installed beacons in other cities, but wouldn’t say which.

Stores have been experimenting with methods of tracking customer behavior via their cellphones’ Bluetooth and Wi-Fi connections, but bringing the kind of shopper surveillance that is common online to the physical world seems to bother people. One coffee chain in San Francisco stopped doing so after its patrons protested. The New York Times reported last year that Nordstrom abandoned an experiment in following customers’ movements around the store in part because people found it troubling.

In June, Apple introduced a “randomization” feature that was supposed to keep iPhones untraceable as they searched for Wi-Fi connections in the area, in order to avoid that kind of retail tracking. But researchers found that feature only worked for the newest generation of iPhones, and even then, only if the phone was asleep and “location” capabilities were turned off for all apps.

In short, the simplest way to avoid physical tracking of your cellphone by ad networks is to turn off your Wi-Fi and Bluetooth when out walking around.

Photo: John Moore/Getty Images