US Patent 7190253 Door control system and method for vehicles

A door control system for vehicles has a transmitter and a receiver for detecting an electronic key in a first predetermined area around a vehicle. A control unit controls unlocking of a vehicle door by determining whether the detected electronic key is an authorized one. The door control system also has an object sensor for detecting an object entering into a second predetermined area covering and wider than the first predetermined area. The control unit activates the transmitter and the receiver only after the object sensor detects the object in the second predetermined area, thereby reducing power consumption.