Locating several Bluetooth users with a typical mobile phone is relatively simple: You just turn on your phone and see which devices are discoverable in your Bluetooth settings. But you can only monitor the people moving in and out of your Bluetooth's range, which is most likely a 10-meter (33-foot) circle around you. If you wanted to track a specific address, you'd have to visually locate that person's physical device and follow it around all day, which would easily blow your cover. And locating someone else's smartphone doesn't let you listen in on what they're doing or read their email.
But If several Bluetooth-enabled receivers are strategically placed to cover a large area, they can track the positions of any discoverable device, recording and sending any data back to a single address. Each Bluetooth receiver acts like any regular Bluetooth device: It searches for every device within range. If a person walked down a 100-meter-long (328-foot-long) street and each Bluetooth receiver had a range of 10 meters, five receivers with a radius of 20 meters (66 feet) would be needed to track that person's movement. As he walked toward the street, the first receiver would track him for the length of the first 20 meters, the second for the next 20 meters, and so on for the length of the street.
So how have people used this system to track people? One of the earliest uses of Bluetooth positioning and tracking technology is the Aalborg Zoo, the largest zoological garden in Denmark, in 2003. The point of installing the system was not to put the zoo's patrons under surveillance or to see which exhibitions people went to more often. Instead, special "Bluetags" were made available to prevent parents from losing valuable belongings that tend to wander off — their children. A parent could attach a "Bluetag" onto a child, and Bluetooth receivers around the zoo would track the child's movement.
Bluetooth beacons (hardware transmitters) have become commonplace for customers to find their way around retail environments. A shopping mall, for example, could install a Bluetooth surveillance system throughout its entire area to monitor the movements of Bluetooth owners. Although it wouldn't present a perfectly accurate description of a person's movement, the system could create a general map of his path and even compare how long someone stays in a certain area.
For instance, in 2018, Bluetooth reported that the giant Mall of America in Minneapolis was using its technology. "With a Bluetooth beacon infrastructure in place, guests can select their destination on the Mall of America app and pinpoint where they are in the facility. From there, the app can get customers moving in the right direction while providing additional information, such as store hours, estimated time of arrival, and vertical transportation factors like escalators that impact accessibility for shoppers utilizing strollers or wheelchairs," the company wrote.
With this knowledge, store owners could analyze shopper's behavior and change advertisement positions accordingly without anyone ever knowing. Some retailers use this surveillance to enhance services, knowing when a shopper with an appointment has arrived and where they are, even in a busy store.
You may have been using this same technology without realizing it. Personal Bluetooth trackers such as the Tile series and Apple's AirTags are very helpful for finding things you misplace often, such as your keys. An app on your smartphone can tell you where they are, as long as they are near another Bluetooth device that can identify the tracker. But this requires many people to have Bluetooth enabled. If you left your keys at your desk, your work neighbor's phone might be able to tell you right where they are. They're doing a kind of Bluetooth surveillance, and so are you — you've opted into the network of people looking for these trackers and passing on that info to someone who may have lost something important.
During the COVID-19 pandemic, several governments have used Bluetooth technology in tracking devices that citizens download on their phones. In the case of Britain, if someone has tested positive for COVID-19 (and the person agrees), the National Health Service will send them a link where they should fill out the contact information (names, addresses, phone numbers) of anyone they have had contact with. The tracing app will then alert these people and may suggest self-isolation depending on the type of contact. The app also lets users know if they are near someone who has tested positive for COVID-19.