A security sensor, or motion detector, is an electronic device that uses a sensor to detect nearby people or objects. Motion sensors are an important component of any security system. When a sensor detects motion, it will send an alert to your security system, and with newer systems, right to your mobile phone.

Home protection and family safety are the primary purposes of a home security system. While this includes detecting burglary, a security system also detects a number of other threats, including smoke, fire, carbon monoxide poisoning, and water damage. When a sensor is activated or faulted, it sends an alert to the alarm control panel. The system will then respond based on the programming settings for that zone.