What is the principle of infrared burglar alarm?

Infrared burglar alarm is a common burglar alarm device, which can judge whether someone passes by by detecting the infrared changes in the environment. The specific principle is as follows:

An infrared burglar alarm usually includes a pair of infrared transmitters and receivers. The infrared beam emitted by the infrared emitter will be reflected by the surrounding objects. After receiving the reflected light beam, the infrared receiver will judge whether there is an object passing by by comparing with the intensity of the emitted light beam.

When something passes by, the intensity of the reflected beam will change, and the infrared receiver will detect this change and remind the user by triggering the alarm device.

The invention has the advantages of simple installation, low cost and no environmental influence. However, because the infrared burglar alarm can only detect the changes of human infrared rays, it can not effectively resist the invasion of non-humans, such as pets or animals.