Microwave Motion Detector

A microwave motion detector is a device that uses Doppler radar to detect and measure the movement of an object. For most people, the two most familiar forms of this mechanism are used in a home security system and in traffic law enforcement. Another familiar application is the use of a microwave motion detector to operate lighting devices upon a person entering or leaving an area.

The microwave motion detector typically is a single unit device that emits a pulse of microwave energy and then detects its reflection. Calculating the time required for the reflection and the change in frequency, it determines the distance, direction, and speed of the object being observed. Direction and speed are computed based on the Doppler effect. Most experience the Doppler effect when hearing a train or other vehicle approaching them; the sound seems to move higher in pitch as the object approaches and lower as it moves away.

In security applications, the microwave motion detector is usually paired with an infrared motion detector. This is to reduce the possibility of false alarms. The microwave motion detector may detect movement of an inanimate object behind a wall or door, such as a windblown tree limb, for example. If the infrared sensor also detects body heat, the likelihood that the object being detected is an intruder is increased, and the security system can execute the required function.