No wiring required for instant operation,2.4 GHz operating frequency.100-150 meters operation distance (free lane).2 - way conversation. (Bi-directional speaking system).Conversation time: Automatic cut off after 90 seconds.Door opening function.Volumn control (Ringing tone).Operated by DC6V, or external adaptor AC230V.Can connect up to 3 sub-indoor units.With incoming call forward function to the sub-unit.