Do Motion Detectors Work Through Windows?

No, motion detectors do not usually "see" through windows. Motion sensors generally use passive infrared (PIR) technology to detect motion. It is very difficult to detect changes in IR energy through glass. And since windows are made of glass, motion sensors don't detect motion through windows.

But there are some rare exceptions to this principle. Old and thin plate glass windows may allow a small amount of infrared energy to pass through, and this could theoretically allow a motion sensor to activate. Or light passing through a window could create enough heat on a particular area to cause a motion sensor to activate. While these situations are quite rare, we do recommend that users install motions facing away from windows for best results.

But for dual-tech motion detectors, the microwave sensors will detect motion through windows. These sensors are able to see through glass and solid objects. Microwave sensors work by sending out microwave signals and taking note of the return rate and pattern of these signals. If there is a change in signal pattern, then the microwave sensor will know that motion is present. However, the motion detector won't alert the alarm system unless both its microwave sensor and its PIR sensor are activated. This helps prevent any false alarms. Please note that microwave sensors can also be adjusted in sensitivity, and properly adjusting the sensor is necessary for ensuring that it works as it should.

Most users would not want a motion to activate through a window. It would be very inconvenient to have a false alarm caused by a passing bird or someone walking by outside. If a user does want to protect a window, they can use a glass break sensor instead. This type of security sensor will actively listen for the sound of breaking glass. If the sensor detects this type of sound, then it will send a signal to the alarm system to alert it of the situation. If any intruder breaks a window to access the inside of the property, the glass break detector will notice. This is advantageous because the alarm actually occurs while the intruder is still outside. Also, if the intruder comes inside, any motion sensors would be able to detect their movement.