Patent ID: 6850148

Claim:
A passive entry having an anti-theft function which comprises a car-mounted transmitter-receiver mounted in a car and at least one portable transmitter-receiver and in which the car-mounted transmitter-receiver generates a wake-up signal and a request signal; upon receiving the request signal, any of the portable transmitter-receivers transmits an answer signal in response to the request signal; and upon receiving the answer signal, the car-mounted transmitter-receiver controls an apparatus mounted in the car, wherein the car-mounted transmitter-receiver has a timer to count time from transmission of the wake-up signal to reception of the answer signal, and wherein the car-mounted transmitter-receiver recognizes the received answer signal as legal only when an elapsed-time value counted by the timer is within a valid elapsed-time value set in advance, wherein the wake-up signal and the request signal are separated by a time interval therebetween, a value of the time interval being changed each time the request signal is transmitted, and the elapsed-time value is varied depending on the value of the time interval.