US Patent 7548160 Anti-theft alarm system for portable computer

An anti-theft alarm system includes a detecting switch portion including a first switch and a second switch, a keyboard controller (KBC), and a key of a keyboard of the portable computer for enabling the alarm system. If the portable computer is moved without deactivation of the alarm system, the second switch opens, causing a change of a voltage at the first switch which is detected by the KBC, the KBC thereby sends an alarm control signal to an audio system of the portable computer, and the audio system produces an audible sound for a theft deterrence effect.