The ultrasonic motion sensor (ultrasonic rangefinder) is designed for use with digital receiving devices. The sensor can be used with the Smart Stairway SS26 step lighting controller. The sensor is designed for installation in a mortise box (hole) with a diameter of 65 mm. The operation of the ultrasonic rangefinder is based on the principle of measuring the time it takes for reflected ultrasound to travel the distance from the rangefinder to the obstacle. The sensor cannot ensure correct operation if sound-absorbing surfaces are used. The processing time of one measurement is 400 ms. To ensure error-free operation, the principle of a differentiated value from three consecutive measurements is used