PIR sensor module (passive infra-red), sensor is an electronic semiconductor type sensor that measures infrared (IR) light radiating from objects in its field of view, this module detects and gives a trigger when there is any motion by a heat radiating object in its range of view.
This Sensor is covered with fresnel lenses, which create a wide angle of detection and also used for noise filtering
PIR includes an adjustable delay before firing (approx 0.5 – 200 seconds) has adjustable sensitivity. It runs on 4.5V-20V power (or 3V by bypassing the regulator with a bit of soldering) and has a digital signal output (3.3V) high, 0V low. Its sensing range is up to 7 meters in a 100 degree cone
This sensor is passive as it does not emit or radiate any energy for detection. Every object above absolute zero emits heat, this heat signature is in Infrared wavelength which cannot be seen by naked eye, but they can be measured by infrared devices