Bluetooth Discoverability

Before we dive into Bluetooth surveillance, we'll want to take a look at how Bluetooth itself works and understand what makes the technology traceable. Bluetooth devices use the free, 2.4-gigahertz radio band known as ISM, which stands for industrial, scientific and medical devices. The band is unlicensed for low-power use, so headsets and other Bluetooth accessories use very little in the way of batteries. While any two Bluetooth devices can share ­data at a range between 10 and 100 meters (33 and 328 feet), phones usually operate at the former, laptops at the latter. Any Bluetooth device can communicate with up to seven other devices at a time.

After you turn any Bluetooth-capable device on, the most basic security feature on it is the ability to go into one of two modes: "discoverable" or "non-discoverable." This information is typically found in the "settings" option of a device's control panel, where you can select whether or not your phone or laptop is visible to others within the area.

If several Bluetooth devices are set on discoverable mode, they all have the ability to search for and locate each other, so long as they remain within range. Every device has its own address, a unique 48-bit identifier with six bytes of information that might look like this: 01:23:45:67:89.10. The first three bytes (01:23:45) are assigned to the specific manufacturer of the device, while the last three bytes (67:89:10) are assigned by the manufacturer. These make each device entirely unique.

Bluetooth Positioning and Tracking

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.

Michael McQueen/Getty Images
Setting up a network of Bluetooth receivers that record the locations of specific makes the method of Bluetooth surveillance possible. Could shopping mall stores do this to track customers' movements?

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.