Passive Infra Red sensors can detect movement of objects that radiate IR light (like human bodies). Therefore, using these sensors to detect human movement or occupancy in security systems is very common.  Initial setup and calibration of these sensors takes about 10 to 60 seconds.

The HC-SR501’s infrared imaging sensor is an efficient, inexpensive and adjustable module for detecting motion in the environment. The small size and physical design of this module allow you to easily use it in your project.

The output of PIR motion detection sensor can be connected directly to one of the Arduino (or any microcontroller) digital pins. If any motion is detected by the sensor, this pin value will be set to “1”. The two potentiometers on the board allow you to adjust the sensitivity and delay time after detecting a movement.

PIR modules have a passive infrared sensor that detects the occupancy and movement from the infrared radiated from human body. You can use this module in security systems, smart lighting systems, automation, etc. There are different PIR modules available in the market, but all of them are basically the same. They all have at least a Vcc pin, GND pin, and digital output. In some of these modules, there is a ball like a lens on the sensor that improves the viewing angle.