Magnetically activated and deactivated vehicle burglar alarm - detects magnetically inserted code known to owner only to allow access to vehicle

摘要

The magnetically activated and deactivated burglar alarm network, particularly suited to vehicle protection, recognises a magnetically inserted code before it allows access to the vehicle. The circuitry is mounted in a box (2) placed inside a windows (1) so that a small magnet (5) can be used to activate the device as required. The circuit consists basically of a counter (9), fixed number generator (11) and comparator (10), in addition to a small audio or visual signal generator (8) and two magnetically operated switches (6, 7). The device is activated by inserting a number in the counter (9) other than that in the number generator (11) by means of pulsing the switches (6, () in a carrier sequency with the hand held magnet (5) using the signal generator (8). any entry to the vehicle in this condition sets off an alarm. To deactivate the device, the counter (9) must first be set to zero, and then have inserted in it a number equal to that in the fixed number generator. This is again done with the magnet(s) via the switches (6, () in a sequence known only to the owner, who knows the etting of the counter and the number produced by the number generator (11).