Which method do PIR sensors primarily use to detect movement?

PIR (Passive Infrared) sensors primarily detect movement by sensing infrared radiation, specifically the changes in infrared levels in their environment. These sensors are designed to monitor the heat emitted by objects within their field of view. When a warm object, such as a person or animal, moves across the sensor's detection area, it causes a change in the infrared radiation level. This change signals the sensor to trigger an alarm or alert.

The correct response highlights the fundamental principle behind PIR operation: the detection of infrared radiation, which is essential for their function in security systems. The sensor does not rely on sound waves, magnetic fields, or climate changes, which are different detection mechanisms used for other types of sensors, such as ultrasonic sensors for sound or magnetic sensors for detecting changes in magnetic fields. Understanding how PIR sensors function is crucial for comprehending their application in security and alarm systems.