It's useful for probing whether the door, window and drawer is opened or moved in illegal.. It consists of wireless alarm and magnet fixed box it can work after the battery is put in, when detecting the movement which is greater than 30mm(opens door), alarm indicator lights(red),and send the alarm signal to the host ,the host (if it's protection state) will alarm with site siren, and automatically dial preinstalled phone to call the police at the same time. When the battery voltage is lower than 7V,the indicator light will bright all the time to remind you changing the battery. Specifications parameter 1: working current: >=12mA 2:transmission power: <=15mW 3:transmission range:150 meters (void zone) (enhanced 300 meters), 4:transmission rate: < 50 ~ 60KHZ 5:static electricity:0 6: frequency deviation:+ -0.1mhz 7: encoding chip :PT2262/EV1530/HOS301/EV1527