Ultrasonic Occupancy Sensor is comprised of a motion detector, electronic control component, controllable switch (relay) and power supply. It emits and receives high-frequency sound waves in the range of 25-40 kHz, well above the range of human hearing. These waves reflect off objects and room surfaces, and the sensor measures the frequency of the waves that return to the receiver. If there is motion within the space, the frequency of the reflected waves will shift slightly; the change is detected by the receiver and the sensor registers a positive occupancy signal. It can detect motion that is hidden from the sensor's view, provided that the space is enclosed with hard surfaces to reflect the waves back to the receiver. It is much more sensitive to movement directly toward or away from the sensor, compared to lateral movements. It works by broadcasting ultrasonic sound waves, analyzing the returning waves and detecting movement through Doppler shifts.