Do Motion Sensors Work in the Dark?

Yes, motion sensors work in the dark. The way that a motion sensor detects movement has nothing to do with how light or dark it is in the immediate area. This is true whether it is a passive infrared (PIR) motion sensor or a dual-tech motion sensor that also utilizes microwave detection.

A PIR motion sensor functions by looking for changes in infrared energy. Every person gives off some amount of IR Energy, which is detectable by a PIR motion sensor. When a person walks within the detection field of a PIR sensor, the device will sense their infrared energy and respond accordingly. Since infrared energy is present and can be detected regardless of the amount of light in the environment, a PIR motion sensor will work just fine in the dark.

Likewise, a dual-tech motion sensor will also work just fine in the dark. A dual-tech motion sensor detects motion by using a PIR sensor and a microwave sensor. The PIR sensor operates in the same manner as a standard PIR motion detector. Meanwhile a microwave sensor works using a principle known as the "Doppler Effect". Both the PIR sensor and the microwave sensor must detect motion in order for a dual-tech sensor to activate. This is helpful for reducing any false alarms that may occur due to environmental issues.

A microwave sensor works by sending out continuous microwave signals. The signals will bounce off of any objects and structures in the area and return to the sensor. If they return to the sensor at a consistent rate, then there is no motion detected in the area. But if there is a change in the return pattern, then the sensor will know that there must be motion in the area. Again, since whether an area is light or dark has no effect on the pattern of microwave signals, a dual-tech motion will work perfectly fine in the dark.