Pyroelectric infrared sensors mainly by a high thermal coefficient of materials such as lead zirconate titanate ceramics, lithium tantalate, titanium sulfate Gambari made the three dimensions of 2 * 1mm detection components. In each detector within the probe into one or two components of the two components in order to detect anti-polarity in series, to contain its own temperature as a result of interference generated. By the detection device will detect and receive the infrared radiation into a voltage signal weak, as in a FET probe with the amplified output field. In order to improve the detection sensitivity of detectors to increase detection range, typically the installation of a detector in front of the Fresnel lens, the lens made of transparent plastic, the lens of the upper and lower divided into two parts, each equal, the system into a special optical system of lenses, it matched amplifier, signal amplification can be more than 70 decibels, so that we can detect 10 to 20 meters of her action. Fresnel lens using a special optical lens in front of a detector changes the turn of the "blind spot" and "highly sensitive area" in order to enhance its detection sensitivity. When someone walked from the lens before, the body issued continually turn the infrared on the "blind spot" access to "highly sensitive area", thus to receive the infrared signal to strong then weak then the form of input pulse, thus strong energy rate. Human central wavelength infrared radiation to 9 ~ 10 - um, and the wavelength sensitivity of detection of components in the 0.2 ~ 20 - um virtually stable. The top of the sensor with the opening of a window film filter, the filter through the wavelength range of 7 ~ 10 - um, well suited to the human body detection of infrared radiation, and for other wavelengths from the infrared filter -rays to be absorbed, thus forming a special purpose of detecting the infrared radiation the human body sensors.