How Do Motion Detectors Work?

Motion detectors are used in a wide variety of places. There are many different types such as radar motion detectors, bugler detectors, sound detectors and infrared detectors. Each type reacts to movement in a slightly different way. Each system is also set up on a different principle. A radar detector that uses a laser beam to detect motion will be set up differently than the average motion light detector. This article focuses on how the infrared motion detector works that most people would place in their yards. This can either be so that they can see better when they arrive home at night, or so that they can tell when something is passing through their yard.

Motion detectors as a passive system

Most motion lighting uses a passive system of detecting energy. This is called "passive infrared" and is sometimes called a PIR detector. A passive system only notices movement, but does not react to it in a harmful way. While some radar detectors might harm someone trying to break in, the passive system only turns on a light. This is still useful for keeping intruders away because many potential criminals will run from well-lit areas. Many people use motion detectors combined with a video surveillance system to keep crime away.

The basic structure

Most motion detectors are set up like a photosensor. An infrared light is used to conduct the electrons off of a substrate and then the electrons can then be detected and changed into the form of a signal. Most detectors look for rapid changes in how much infrared energy is detected. This means that objects have to be traveling at a rather fast speed to be detected. Otherwise, the motion light would go off when nearly anything happened, such as changes in air temperature.

The "seeing" lens

Motion lights have an attachment that uses an infrared lens to "see" the motion. Because infrared is a part of light, it is possible to detect motion through the use of plastic lenses. Usually one or two infrared sensors are used to detect the changes in the infrared light.

Motion detectors and glass

Infrared energy cannot be easily transferred through glass. If glass separates the motion detector and a place that it should be able to see, it will not be able to detect any movement through the glass.

Setting up a motion detecting system

Usually motion detectors are sold either as a socket for a light, or as an attachment that can be added to a light socket. For maximum benefit, it is important to find gaps between the different motion detectors. Try to set up your system so that it isn't possible to go around it and not set off one of the sensors.