For some devices, protection is more important than detection. We want to keep someone from stealing certain systems or information at all costs. But for other devices, it may be enough to detect that an attempt has been made to access or steal hardware or software. For example, chaining down a disk makes it unusable. Instead, we try to detect when someone tries to leave a protected area with the disk or other protected object. In these cases, the protection mechanism should be small and unobtrusive.
One such mechanism is similar to the protection used by many libraries, bookstores, or department stores. Each sensitive object is marked with a special label. Although the label looks like a normal pressure-sensitive one, its presence can be detected by a machine at the exit door if the label has not been disabled by an authorized party, such as a librarian or sales clerk. Similar security code tags are available for vehicles, people, machinery, and documents. Some tags are enabled by radio transmitters. When the detector sounds an alarm, someone must apprehend the person trying to leave with the marked object.