Support intercommunication of up to 999 intercom phones. Working frequency: 410MHz-460MHz with 20 channels. Working distance: up to 1km without any block. Call ID number display and screen flashing for missed call. Ring: 38 ringtones with adjustable loudness. Adjustable speaking voice. Two working modes: a) Plug in 5V1A b) The battery works Battery 2000 mAh working time-about 60 days standby current 1mAh. The host has one-click automatic broadcasting function. External audio broadcast intercom function. Extension has one-click host calling function. Product size: 160mm x 110mm x 20mm