... doorbell 1. very cheap price 2, easy installation 3, very clear voice and long distance 4.with unlocking fuction 1. IntroductionThis ... up the microphone, can call outdoor , both sides of the clear communication, there is two intercom calls such as special line ... wires. the two wires are exchangeable.long operating distance, loud and clear sound.the electromotion-lock needn't to connect with extra ...