Passive remote access control system

摘要

Access to a motor vehicle (23) is controlled by periodically transmitting an interrogation signal (43) from a control circuit (22) on the vehicle (23). Upon receiving the interrogation signal (43), a hand-held remote control (21) transmits a reply signal to the control circuit (22). The control circuit (22) measures the strength of the reply signal and the activates a first function (30), such as unlocking a door of the vehicle, when the strength exceeds a first threshold level. Thereafter, when the signal strength exceeds a second threshold level, the control circuit (22) activates a second function (30), for example enabling the engine to be started. When the signal strength drops below a third threshold activates a third function (30), such as locking the door.