PIR sensors, also known as Passive Infrared sensors, are used by a microcontroller to sense motion usually by a human being, but they will detect any motion within the range of the sensor. These sensors are small, inexpensive, low-power and easy to use, which makes them perfect for beginners to experiment with, but industrial versions of these sensors can also be found in many consumer and military products as well.
PIR sensors are made of pyroelectric sensors that can detect infrared radiation levels. Every object that has a temperature above absolute zero emits some low-level infrared radiation that the pyroelectric sensor can detect. The passive part of the name means that the sensor does not generate or radiate energy that can be detected by other devices. Instead, it works by detecting the infrared radiation emitted by other objects.
The pyroelectric sensor in...