After a door of a vehicle is locked, a touch switch and a lock switch is disabled for a predetermined time period. A predetermined operation of a holder of a handheld unit to a door handle during the predetermined time period causes a device mounted in the vehicle to perform a certain function other than unlocking the door. Thus the predetermined operation solely to the door handle after the door of the vehicle is locked can serve as an instruction for the device mounted in the vehicle to execute the certain function.