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An infrared motion detector uses infrared sensing to detect motion in a given area. This type of detector is often used as part of a larger security system, typically including the detection as a way of triggering alarms that indicate a potential issue to security or emergency services. The use of infrared technology usually allows such a detector to only pick up on heat and therefore more easily ignore non-living motion. An infrared motion detector can also be set to only pick up on certain levels of heat, making it possible to ignore small animals.
Infrared light is a spectrum of non-visible — for humans at least — light that is emitted by objects when they produce heat. Different levels of heat production can create varying levels of infrared emission, and other types of technology often use infrared beams to transmit information wirelessly. Television remote controls, for example, often used infrared light to send a signal between the remote and the television receiver. Body heat, from a living creature, produces infrared light and an infrared motion detector is able to pick up on this release of energy to track motion.
Typical motion detectors often suffer a flaw of picking up on any kind of motion. This means that someone with a motion detector outside his or her house will have cars that drive by trigger the motion detector, as well as tree limbs swaying in the wind. An infrared motion detector, however, only tracks motion that also emits infrared energy, and therefore is able to ignore non-living and cool organic materials.
This allows a security system utilizing an infrared motion detector to only trigger and activate a light, alarm, or other security system if there is motion from a living creature. Someone living in the woods, for example, may want a motion detector to activate a bright light to keep wild animals, such as raccoons, away from a house. The use of an infrared motion detector in this type of system would allow the activation of the light to scare away animals but not have it come on whenever a strong wind blew tree limbs around.
An infrared motion detector can also often be designed to only activate when certain levels of heat energy are detected. Such a detector can be set to only activate when heat levels from a living creature over a certain weight limit are in motion. For an indoor motion detector, this can allow someone to set the infrared detector to only activate an alarm if a person passes through a room, but ignore smaller animals like a cat or dog.
Walking around the neighborhood at night I always wondered how those motion detector lights worked that switch on when you walk past certain houses. They always manage to startle me, so I think I might invest in them for security as well!