A portable device in an electronic key system has a motion detection sensor to detect its motion from a continuation of standing state over a specified period of time, sound and vibration are generated. This sound and vibration make the user aware that he or she carries the portable device. The user thus is reminded of carrying the portable device whenever he or she goes out. If the motion detection sensor detects a larger motion, the sound and vibration are generated without checking the specified period of time. The motion may also be reported to handy equipment, which is separate from the portable device and carried by the user.