Patent ID: 7791457

Claim:
A method for identifying unauthorized access to a vehicle having a keyless-passive entry system, the method comprising the steps of: broadcasting an interrogation signal from a vehicle based transmission device of the keyless-passive entry system, the interrogation signal having a first pulse transmitted at a first amplitude and a second pulse transmitted at a second amplitude where the second amplitude is greater than the first amplitude by at least a predetermined difference threshold; receiving the interrogation signal by a portable communication device of the keyless-passive entry system; determining, by the portable communication device if the second amplitude of the second pulse is greater than the first amplitude of the first pulse by at least the predetermined difference threshold; and determining, by the portable communication device that the interrogation signal is an authorized interrogation signal in response to the determination that the received interrogation signal includes the first pulse transmitted at the first amplitude followed by the second pulse transmitted at a second amplitude where the second amplitude is greater than the first amplitude by at least a predetermined difference threshold.