Car burglar alarm

EE 62 February 1986 CAR BURGLAR ALARM Although no alarm offers complete protection against theft, it will, none the less, deter most thieves and joyriders. The alarm described here, once set, can only be disabled by a four-digit code; even cuffing its supply cab/es will set it off The alarm may be triggered by the door contacts for the courtesy light, an infra-red sensor, a vibration detec- tor, or an ultrasonic sensor. In ad- dition, the circuit reacts to any small voltage drop across the car battery, for instance, when the courtesy light comes on. Even if the thief discovers the whereabouts of the alarm and smugly cuts the supply cable to it, he has gained nothing, for not only has the alarm already been triggered, but also the ignition circuit has been broken. There are only two ways of deactivating the alarm: typing in the correct four-digit code on a small keyboard within 15 seconds from opening the door, or disabling the car. The latter is obviously not the in- tention of th...