Infrared Detectors

Passive infrared detectors pick up on temperature changes caused by an intruder. To cut down on false alarms, they must detect both motion and a rapid change in temperature. Infrared detectors use either a mirrored or a fresnel lens to focus the infrared rays emitted by a moving person, animal, or object in the detector’s field of view onto the detector’s pyro-electric sensor.

Some passive infrared detectors are battery operated and transmit a wireless alarm signal to a receiver connected to the burglar alarm panel.

Infrared detectors were used in high security applications in the 1970s. The PR 851, with a protection range of 40’ x 30’, even protected the US Mint. The ceiling mounted DR 569, produced in the late 1980s in Framingham, MA, had a pattern of twelve 60’ curtains.

Many older infrared detectors are still operating in alarm systems globally. The next time you’re in a retail store, look up at the ceiling or wall and see if you can spot one.