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How do motion-sensor alarms work?

There is a wide variety of movement sensors out there, including indoor and outdoor motion sensors, as well as passive and active sensors, both of which use different technologies.

Passive sensors emit radioactive energy, then monitor the space, while active sensors monitor the area for any changes in that space’s energy patterns. To identify motion in that space, active sensors can emit three different kinds of energies: microwave radiation, sound waves or infrared light.

Different types of motion-sensor alarms have the same goal: to detect the presence of an intruder and send some kind of alarm or alert to the monitoring centre.