Abstract: An electronic anti-theft system for vehicles having a common signal generator and speaker for both the alarm siren and the arming chirp, in which the volume of the arming or disarming chirp can be set to a desired level. A control circuit is detailed which allows the volume of the arming chirp to be attenuated.

Abstract: A vehicle security system includes a transmitter, a receiver, a timer, a controller and an alarm circuit. The transmitter transmits selectively an encoded signal when activated by the user. The receiver develops a decoded signal in response to reception and recognition of the encoded signal. The decoded signal has a reception time duration commensurate with a transmission time duration of the encoded signal. The timer develops a momentary timer output signal. The timer output signal is developed in response to initial application of the decoded signal to the timer in the absence of ignition voltage and is developed after a selected timer duration in response to continuous application of decoded signal to the timer and the presence of the ignition voltage only if the reception time duration exceeds the selected time duration. The controller develops a binary signal. The binary signal switches states in response to each occurrence of the timer output signal.