... intercom voice volume, brightness, contrast adjustment, calendar time, inside buy a variety of chord tones, pictures, video and other functions ... the indoor and outdoor machine free form 1 to 1, 1 to 2,2 in 1, 2 to 2, 2 to 4, to meet the needs of different users; two ... electronically controlled lock automatically open, there is no need to go to the door to open, if the room no answer, indoor machine ...