The most common type of motion sensor used in home security is a passive infrared sensor, otherwise known as a PIR sensor. PIR sensors send out rays designed to detect heat. The sensor’s rays fan out, so they’re most concentrated right next to the sensor, and become less sensitive farther away from the sensor.

Occupancy sensors activate lighting once an occupant is identified. Once the occupant has left, the sensors automatically turn the light off. When leaving a room occupants can neglect to turn the lights off. This will end up costing you more and is hardly energy efficient. 

The principal advantages of employing occupancy sensors are :

Security

Energy Efficiency

Convenience

https://www.acelectricohio.com/benefits-of-having-motion-sensor-lights/