Types of Occupancy Sensors Used for Burglar Alarms

Ultrasonic

• Ultrasonic occupancy sensors work by emitting high-frequency sound waves that are above the limits of human hearing. According to EC&M, these waves bounce off of surrounding objects, and then return to the mounted the units--which emitted them--for analysis. Changes in the frequency of the returning waves indicate that there is motion, and will trigger the light, or lights, connected to the occupancy sensor to turn on. In many instances, an ultrasonic sensor will not need a direct line of sight to detect movement, meaning that it can detect movement even if it occurs behind an object, or around a corner. However, walls comprised of fabric components may pose a challenge to this capability. Other drawbacks include a tendency for the ultrasonic sensors to nuisance switch, or go of accidentally, when there is a strong amount of airflow in a space or if there are vibrations.

Passive Infrared

• Unlike their ultrasonic counterparts, passive infrared, or PIR, occupancy sensors require a direct line of sight in order for them to be effective. According to Home Security Guru, this is because the PIRs do not emit any energy, but instead collect it in the form of infrared heat using lenses and computer chips. In a single PIR sensor, the lens captures heat emissions from the area it is pointed at, and then transfers them to a specialized chip that can detect hotspots. These hotspots indicate that an object significantly warmer than its surroundings, such as human body, has entered a space. Drawbacks include warm-blooded pets like dogs and cats causing false alarms. However, you can bypass this problem by installing a system designed to ignore floor-level heat changes.

Dual-Technology

• A dual-technology occupancy sensor is one that incorporates both ultrasonic and infrared technology. The sensor only triggers lighting to go on when both sensor components confirm, with their individual methods, that there is movement in a particular space. The dual approach helps eliminate the chances of your sensor nuisance switching, as the ultrasonic and infrared technologies have each other to fall back on. This also makes it harder for burglars to sneak by a sensor undetected.