Patent ID: 7498928

Claim:
An electronic key system for a vehicle, comprising: a control unit mounted on the vehicle, wherein the vehicle is a motorcycle; and a portable transmission/reception device for transmitting an answer signal in accordance with reception of a request signal from the control unit, wherein the control unit comprises: first means for outputting the request signal to the portable transmission/reception device at transmission intervals corresponding to a traveling state of the vehicle, wherein the traveling state includes a vehicle speed, and acceleration/deceleration, the first means shortens the transmission interval of the request signal corresponding to an increase of the vehicle speed, the first means shorten the transmission interval of the request signal corresponding to an increase of the acceleration/deceleration, and wherein the vehicle speed and the transmission interval of the request signal are set inversely proportional to each other; second means for detecting the answer signal caused by the request signal from the portable transmission/reception device; and third means for outputting a warning at a point after the detection of the answer signal in the second means stops.