Antitheft circuit for vehicle - has coil which senses load current flowing in RC circuits, shunting internal lights

摘要

The antitheft circuit has a wire (11) passing through a sensing coil (31) that actuates an alarm. The wire is a supply wire connected to one pole of the vehicle's battery (10). The other pole is connected to a second wire (12). The two wires are joined by a set of parallel circuits. Each circuit comprises the series combination of an antitheft contact (16 etc.) and an RC circuit (23,24,etc.). Each RC circuit comprises a capacitor shunted by a resistor and acts as a load drawing current from the battery when an antitheft contact is closed due to unauthorised entry to the vehicle. The current passing through the wire (11) is detected by the coil. The RC circuits are connected in parallel with the internal lights (13-15) of the vehicle. The alarm system is independent of whether the lights are defective (open circuit) or not.