Locating several Bluetooth users with a typical mobile phone is relatively simple: You just turn on your phone and search for every discoverable device. But you could 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.
Creating a Bluetooth surveillance network solves this problem. 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. 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.
Some people worry about others using this sort of technology illegally and maliciously. 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. With this knowledge, store owners could analyze shopper's behavior and change advertisement positions accordingly without anyone ever knowing.
It's difficult for someone to use Bluetooth to identify you in particular, unless you've chosen to include your name or some other personally identifiable information in the name of your phone, smart phone or PDA. Still, if you're concerned that someone might be able to track you down via Bluetooth, the best defense is to make your device non-discoverable to others when not using it.
For lots more information on Bluetooth technology, see the next page.