Siedle Basic audio set in bus technology with the functions of calling, speaking and door opening. Number of call buttons: 1 Each basic set can be expanded to include selected door and indoor stations, as well as switching functions and a telephone connection. Scope of delivery: . Siedle Compact audio door station (CA 850-1 E) . Siedle Basic audio indoor station (AIB 150-.) . Set power supply unit (SNG 850-.)