Telephone exchange system with switching device

摘要

The telephone exchange system includes a door station (5) with a call recognition device (6), a door intercom (10), and a door opener (16). The door station includes a detector (18,19), which recognises a connection to the door station and enables free switching of the door intercom apparatus. The call recognition device preferably uses an electric switch (7) for coupling the exchange (2) to the door opener. The detector is coupled to the call recognition device to effect the breaking of the electric switch. Typically the detector recognises an audio tone and is coupled to the door call apparatus to effect a volume reduction of the door intercom.