Digital audio telephone is used for communication with outdoor panel, phone to phone intercommunication, release of electric door strike and also door bell option. The system is able to operate up to 120 BUS-2 audio telephones (primary and secondary telephones). Each main - primary telephone has to be identified (programmed) with a system number which assigns the telephone to a precise push button on the outdoor panel or to a code dialed on the keypad of the outdoor panel. There can be other 3 additional – secondary audio telephones connected to the primary telephone with the same user operation features. They have the same logical address as the primary one – they are assigned to the same push button or code. This allows installing up to 4 audio telephones within one flat or office premises.