Patent ID: 6489886
Filing Date: 2002-12-03
Classification: B60R

Abstract:
A security system to prevent unauthorized operation of a vehicle comprising:a vehicle control unit comprising a transmitter and a receiver and being responsive to a control signal to transmit an interrogation signal; a remote transponder comprising a receiver for receiving the interrogation signal and for generating a DC voltage to operate the transponder and a coded signal therefrom, a signal strength detector having a plurality of threshold levels receiving the coded signal and a code checking circuit receiving an output of the signal strength detector to determine if a code in the coded signal matches a stored code, the code checking circuit, on determining a match, changing the threshold level of the signal strength detector from a first to a second level which permits only signals of a predetermined strength to be received, whereby the predetermined signal strength is indicative of the transponder being at a chosen location within the vehicle; and a transmitter in the transponder transmitting an authorization signal to the vehicle control unit to authorize the operation of the vehicle if a properly coded interrogation signal is received at the second threshold level.