A motion detection system includes a first motion detection device that detects a motion of an object based on a reflected wave of a radio wave transmitted by a first radio wave sensor, the first motion detection device including the first radio wave sensor, and a second motion detection device that detects the motion based on a reflected wave of a radio wave transmitted by a second radio wave sensor, the second motion detection device including the second radio wave sensor, wherein one motion detection device among the first and second motion detection devices transmits a determination radio wave and another motion detection device among the first and second motion detection devices receives the determination radio wave, and wherein only the first motion detection device is used to detect the motion when received intensity of the received determination radio wave is smaller than a predetermined threshold.
Motion detection system and motion detection device