Pyroelectric infrared sensor is mainly composed of a kind of tall thermoelectric coefficients of materials, such as zirconium lead titanate department ceramics, litao3, acid three made gedaliah titanium size for 2 * 1mm detection devices. In each detector loaded within one or two detection devices, and two detection with the polar components in series and to suppress because of its own temperature rise of interference. By detecting components will explore and receive the infrared radiation into a glimmer of voltage signal, the outfit is in probe inside the mosfet enlargement outward output. In order to improve the detection sensitivity in order to increase the probe detecting distance, be in commonly the probe ahead furnish a Fresnel lens, using the Fresnel lens special optical principle, the probe ahead produce a variations of the "blind" and "high sensitive area", in order to improve its detection rx sensitivity. When someone from the lens body before walked out of the infrared ray continually alternate from "blind" enter "high sensitive area", this makes receives the infrared signal to suddenly suddenly weak pulse form strong input, thus strong its energy prices.