pir sensor analog or PIR , pyroelectric infrared sensor, is normally known as a motion detector. It is a passive sensor based on measuring infrared light radiating from objects within its field of view. The detector itself cannot emit infrared. It is commonly used in burglar alarms and smart lighting applications.
Normally PIR works with a fresnel lens. The human body has a constant body temperature, which is different from the ambient temperature. When a human body moves, this difference is detected by PIR through a Fresnel lens, which outputs an signal.