Motion sensor(PIR) is a passive infrared detector or physical sensor. This sensor doesn’t emit any energy but only passively receive and detect infrared radiation from outside.
Whenever sensor detects a motion it triggers light to turn on and when there is no motion it makes light to turn off
Motion sensor can also works a security sensor, when you are not at home then if there is any motion happens it Triggers siren and sends you a notification.
This Motion sensor also comes with a Light sensor so you can turn on Lights based on the Light sensitivity