Car Tilt Alarm

00 Many cars are fitted with some sort of alarm system as protection against petty criminals and joy riders. Most of these systems rely on a door switch and one under the bonnet (to prevent inter- ference with the battery connections to immobilize the alarm system). Such systems afford no protection whatsoever to another criminal pest: those who jack up the car and remove expensive alu- minium sports wheels. The circuit described here is an add-on to an existing alarm and energizes this when the position of the car is changed, for instance, by a jack being placed under it. The position of the car is monitored by four mercury switches which are placed in such a way that when the car is horizontal they are open. Because a car is sometimes parked in an inclined position, which causes one or more of these switches to close, some additional circuitry is necessary. The four D-type bistables in IC, deter- mine the output state of the mercury switches. The outputs of IC, are con- nected t...