Security Tips and Industry Musings

Motion Detectors

Lew Stouffer - Monday, October 13, 2014

The most commonly used motion detector in alarm systems uses passive infra-red (PIR) sensors to detect movement. These sensor are sensitive to the surface temperature of the object in contrast to the background’s temperature. Some higher end motion detectors are dual technology devices. These devices add a microwave emitter to the PIR detector. The microwave emitter operates on the same principle as Doppler radar.  Both sensors would have to indicate movement in order to go into alarm, thereby reducing false alarms.

Motion detectors are ideally used as “internal traps”. What this means is they are used as another layer of the security system in case the previous layer is penetrated. For instance if a window contact is bypassed, the motion will alert you as the intruder moves through the viewing area.

When deciding on the placement of motion detectors consideration for the way you live in the home, children and pets must all be taken on account. For instance, while a hallway is a great place for a motion detector to catch an intruder it is a difficult place to have one if your children may get up to get a glass of water in the night. Likewise if you have pets that you allow to roam the house, a motion detector may not be a good fit. With some thought there are compromise solutions available in most cases.