This is Active Infrared .Install each pair at the opposite positions.Then there is a infrared area between these two parts. When someone the infrared region, the will send alarm to the security alarm host. Outdoor alert up to 10m, indoor alert up to 20m. Great to be installed for in school, office building, hosipital, home yard, etc. range can be reduced to 30% in bad weather conditions, like rain, , etc. Features: - Color: Black. - Material: ABS. - Quantity: A pair. - Outdoor guard distance: 10m. - Indoor alert distance: 20m. - Sensing speed: 30ms. - Alarm Output - Normal: NC & NO capacity / DC 30V / 0.5mA. - Alarm linkage: Yes. - Working voltage: DC12-24V. - Through CE, , ROHS, IP55 . High level of resistance to RFI / EMI. - Outdoor alert up to 10m, indoor alert up to 20m. - Professional - optical cover, unique digital filter circuit design, with rain cover design. - Adjustable beam interruption period to make it more flexible and adaptable. - -glare up to 50,000LUX, built-in automatic adjustment of light filter system, to avoid the impact of light or car lights, all-weather sealed (rain), (insects) and other all-weather integration of the structure designed to work in harsh environments. Package list: 2 x -theft Alarm Warning Single Beam Alarm Infrared Radiation For Indoor Or Outdoor Rain Cover Infrared Alarm for (a pair of Black)