Keeping a Bluetooth device in "discoverable" mode allows other gadgets with Bluetooth to locate it within a certain range.

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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.

So how could someone track your movement if you left your phone on discoverable? Would they have to follow you around all day long, or is there a simpler way? To learn how a Bluetooth surveillance network is set up, read the next page.