Keyless entry system with radio card transponder [automobiles]

A keyless entry system for locking and unlocking vehicle doors, and for opening the trunk is described. This system utilizes a small (ordinary credit-card size) card transponder with a built-in personal identification code that can be carried in a pocket or a briefcase and the user does not have to take it out for use because the signal transmission is effected by inductive coupling between the card and loop antennas built into the door mirror housing and rear bumper. By touching a switch provided near the trunk keyhole, the user can open the door or trunk as if there were no locks. For anti-theft security and reliability, the system incorporates a twin-loop antenna that generates a rotating magnetic field, and a detection system to prevent the card transponder from being left inside the vehicle. This system has been installed in the luxury classes of Nissan models in the Japanese market