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- The most commonly used form of motion detection is infrared which is a light beam below the red end of the color spectrum and undetectable to the human eye. An infrared detector is monitoring an area for heat movement. Every living thing gives off ambient heat, including plants. When the beam senses heat motion it can activate lights, sirens or surveillance cameras, depending on how the system is set up. The sensitivity can be set so that it doesn't set off alarms every time the wind blows but must be triggered by a more significant event.
- Microwave sensors emit short electromagnetic waves that are longer than infrared waves and shorter than radio waves but are still below the light spectrum that can be seen by the human eye. A microwave motion detector sends out intermittent signals that are bounced back to a sensor. When the microwaves return, the waves are reflected from different locations as an object moves through them. The sensor detects the change. Again, depending on the system, it can activate alarms, turn on lights or swivel cameras to the location of the movement.
- Pressure plates can be built right into the floor of a home or any sensitive area of a store or business. Pressure plates are purely mechanical. They are probably the simplest technologically of all motion detection systems. The simplest types work by laying circuitry through the flooring, leaving the circuit open. When pressure is applied in a particular area or multiple areas, it completes the circuit and sets off an alarm, lights, cameras or whatever alert system is chosen. It works like a light switch. All the wiring is in place to turn on the light except the circuit through which the electricity runs is left "open" by the switch. When you turn on a light switch, it closes the circuit and allows electricity to flow throughout the circuit and, presto, the light comes on.
- Cameras can be mounted for surreptitious surveillance, hooked up to broadcast their signals live to remote viewing monitors and/or taped to preserve evidence. For home use, some people place the cameras in auspicious locations as deterrents for would-be burglars. Often they're not even operational. It's cheaper that way. For surreptitious surveillance, motion-triggered cameras can be located in the most inauspicious of places; if you want to keep an eye on your children while at work, for example. As a general rule, the smaller they are the more expensive.
- No one system is infallible alone. If security is a high priority, it is recommended that some combination of security systems be used. The Best Buy store in New Brunswick, New Jersey, was burglarized overnight in March, 2010, and $26,000 in laptop computers were stolen despite the store's motion detecting cameras. The motion detectors were set to detect floor-level motion while the thieves cut a hole in the roof and rappelled from the ceiling to the racks where the laptops were taken. They further shielded their presence behind store banners hanging along the ceiling. Simple systems can be fairly inexpensive but the more complex and the more systems that are installed, the price rises dramatically.
Infrared
Microwave
Pressure
Video Cameras
Combinations
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