PIR (Passive Infra-Red) detection is a technology used in security systems to detect movement or intruders by recognising light emitted from nearby objects.

PIR motion detector / sensor works by having two horizontal sensing elements and measuring the rate of infrared light change between the two elements.

PIR motion detectors / sensors come in two types:

• Thermal infrared sensors: Thermal infrared sensors or pyroelectric infrared sensors use infrared as a heat source to detect objects. Their sensitivity is independent of wavelength. Detection time and response speed is slow.
• Quantum infrared sensors: Quantum sensors detect photons, depending on wave length, and are more sensitive than those that sense heat. These sensors are fast in detection and response, while requiring frequent cooling to make accurate measurements.