Visitors call indoor monitors through Outdoor station, and residents can make clear video calls through the indoor monitor with visitors. Digital audio & video transmission is more stable and reliable. Including old buildings with 2-wire non-polarity connection, Existing wiring in the house without re-wiring. Easy installation central power supply without using adapter. Power and intercom signal is transmitted in 2-wire. Visitors recording and leaving message option. Also speech for viewing and speaking at the same time, an option to read an elevator from the indoor monitors or send an elevator to a visitors. Possibility to add IP cameras to the system. The system in English /Different language is easy to install.