Abstract: An anti-theft alarm is provided, for a portable device such as a laptop computer. An embodiment of the anti-theft alarm comprises three main components: a uniquely coded tag for attachment to the bottom of the device, a pad upon which the device is placed, for sensing the tag, and an electrically powered control module. The module is connected to the pad. The control module is able to determine if the tag is still in contact with the pad--if not an alarm sounds immediately. The module can also determine if the electrical power has been disconnected and if the module has been moved (using a motion sensor). If there is no power and the module has been moved, an alarm sounds immediately. The alarm can be disabled with a key switch.