Plug into 220 AC power. Or, insert 4 cells of R6P SIZE AA1 .5V (alkaline) into the cabinet of either one of the talkback pair. When you want to have a talk with the other , press down the push button and bell of his or her set will ring no matter whether you take up your handset or not. While talking, please speak into the micro phone. When the talk is over, put back the headset, See to it that the pilot light is off, or else the talkback set is still in working condition and continue to consume electric power. Our talkback are convenient to connect by means of twin conductor to common use, while connecting, please pay attention to the color of the two different conductors. The effective talkback distance is 3 kilometers, with wire resistance less than 60 ohms. The ring sounds level can be selected.