BMotion detectors automatically switch on the light when they detect movement at night, thus creating security. The reliable helpers usually work with a passive infrared sensor, which detects the thermal radiation of living beings. Humans lie in the infrared wave range and are not visible to the naked eye. Motion detectors only detect larger movements, they do not provide any information as to where exactly the activity took place and, as the name suggests, they are trained for movement and not for the presence of living beings.
A similar type of device has been around for some time and is now becoming popular: Presence detectors are the better motion detectors. They detect the smallest movements and can thus reliably detect the presence of a person. In addition, they identify the spatial location of one or more persons as well as a direction of movement and a range of distance. Compared to an infrared sensor, presence detectors have two disadvantages: They do not run on batteries, so they require a fixed power supply, and they take around 300 milliseconds to trigger instead of just 3 milliseconds as with the infrared sensor.
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