Imagine you are walking in the darkness...suddenly, a light switches on, and the front door opens itself as soon as you reach the entrance. These are the little tricks of an infrared sensor.

Infrared is a kind of invisible light, existing outside the red part of the rainbow. Its wavelength is longer than that of visible light, and it is also called a "heat wave," since it is more heat-effective than visible light. The human body also emits infrared waves, and their wavelength is dependent upon a person's body temperature. The wavelength of approximately 36.5 degrees Celsius is 6-14 micrometers, for example. Infrared sensors detect only infrared. They can be made smarter, however, so that they detects only human bodies, by attaching a filter related to the wavelength of the human body's infrared waves.

This is called the Fresnel-IRDET Human-Movement Sensor. This technology is used not only for automatic doors, but also for security lighting equipment and self-activating lights for energy