What is a motion detector primarily used for?

A motion detector is primarily designed to detect movement within its coverage area. This is achieved through various technologies, such as passive infrared sensors, which identify changes in infrared radiation caused by moving objects, or microwave sensors that detect changes in microwave energy as objects move. These devices are commonly employed in security systems to activate alarms or alerts when unauthorized movement is detected, thereby enhancing security by monitoring for potential intruders.

Other options relate to different functions not served by motion detectors. For example, detecting smoke is the role of smoke detectors, which use specific sensing technology to identify particles produced by combustion. Monitoring temperature changes is typically done by temperature sensors, while activating fire alarms usually involves interconnected systems that include smoke detectors or heat detectors to respond to fire hazards. Each of these devices has distinct purposes separate from the function of a motion detector.