Types and Operation of Motion Detectors

Motion detector systems use a variety of methods to detect movement. Each method has advantages and disadvantages. Infra-red detectors sense heat, and can detect an intruder’s radiating body heat. Most infra-red detectors are passive, meaning they do not send out signals but merely receive signals, such as changes in temperature. Microwave and ultrasonic detectors are active—that is, they send out waves of energy and receive waves reflected back by objects. Any disturbance in the reflected waves caused by a moving object will trigger an alarm. Video systems optically monitor an area, and movement is registered visually on a monitor. Often, these methods are combined to improve accuracy and reduce chances of a false alarm.