As the definition goes, a motion detector or an alarm detector detects motion. It can be either motion of things or motion of people. When a motion is detected, it gives an input to either an alarm or a warning signal. Any alarm detector should work along with a sensor which is the interface with the real world. The sensor senses the presence of articles or people and also senses the motion of them. Then, the sensor gives an input to the alarm detector which gives out an alarm.
One example of a motion detector is one which has a beam of light running through and a sensor fitted on the other end. Once a customer walks through, the sensor is able to detect a difference in light and gives an input to the detector. This alarm detector basically works on the principle of amount of light received.
Automatic door openers have simple radar which releases a burst of microwave energy and waits for the reflected energy to bounce back. When a person crosses, the reflected energy is scattered and the amount of reflected energy is less than the normal conditions or the time taken for the reflected energy to travel back is more and an alarm goes off.
This is termed the ‘echo’ technology. It can be used with microwave, ultra sound, infra red forms of waves also.
The above class of alarm detectors, all of them fall into the category of ‘active sensors’. They inject light or energy and wait for the reflected energy to take decisions. There are also other classes of alarm detectors which are termed ‘passive sensors’. These detect the presence of light. A human being with normal skin temperature of 93 degrees Fahrenheit typically emits infrared waves of wavelength 8 to 10 micro meters. Hence, an infra red sensor of range 6 to 12 micro meters is particularly sensitive to human movement. Also, these lights do not operate if the person is standing still. It is because these alarm detectors detect change in the amount of infra red received rather than continuous monitoring. There should be a rapid change in the amount of infrared waves indicating human movement.
One other application of this alarm detector is the car alarm which goes off when anyone bumps into the car or comes too close to it. It works based on the infra red alarm detector which detects body heat in the form of infra red waves which is tapped by the sensor. Outdoor alarm detector also work on the infra red sensor causing a particular area of the drive way to be illuminated only when a person enters. However, it could also prove to be a nuisance with the presence of squirrels, dogs and cats moving across the place.
Installing an outdoor motion sensor security light is not hard, watch as Eric installs an outdoor motion detector light, showing the wiring and installing an exterior motion light. And of course, the Labrador Retrievers help.
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