Used for prevent the door or windows is opened illegally, composed with transmission and receiving two parts. When the distance between the transmission and receiving is over 3cm,the LED lamp will be on and send signal to the main control panel to alarm and dial the preset telephone numbers. Specifications: (SC-2003A-I) .Power supply: DC9V battery .Working frequency: 315MHz/433MHz .Gap for triggered, >15 -20mm .Stand-by current: 0.01W .Alarm current: 0.09W .Working temperature: -10 ~ 50 .Relative humidity: 95% .N.W.: 45g