Multi-user intercom 4-way kit. Build-in microcomputer-controlled circuit and coding and decoding digital circuit. Only 4 cables for connecting all the units with stable performance and anti-interference function. Intercommunication is available between indoor phones with privacy kept. Busy line reminding and ring-off indicating Centralized power supply. Clear voice. Maximum talking distance: 300m. 4-wire connection. Enclosed an adapter. Accessories Four interphones     One transformer Four brackets           Screws Wiring Diagram