If pressing the bell button is supposed to activate other functions as well, an a/b switching module – available for the TFS-Dialog 200, TFS-Dialog 300 and TFS-Universal plus – pays off immediately: it takes care that e.g. the light in the hallway goes on or the existing door bell rings. The modules are simply interconnected at any point of the signal line between door intercom and the a/b port of your telephone system.
When the bell button is pressed, a special control signal triggers the desired switching process. If e.g. you are talking to the visitor at your front door, you can release the door opener by pressing a key on your phone. And if you install several a/b switching modules, you can control various switching processes with different frequencies.