If you want to activate other functions with the simple press of the doorbell, an a/b switching module – compatible with TFS-Dialog 200, TFS-Dialog 300, and TFS-Universal plus – is worthwhile: It ensures that, for example, the hallway light is turned on or the existing doorbell is activated simultaneously. The modules can be easily connected at any point on the signal line between the door intercom and the a/b port of the telephone system. When the bell button is pressed, a special control signal is generated that triggers the switching process. If you are currently speaking with the visitor at the door, you can open the door by pressing a number key. If multiple a/b switching modules are to be used, different switching processes can be controlled by specifically addressing them with different frequencies. Up to six of these a/b switching modules can be used with a TFS-Dialog 200/300 door station, and only a single two-wire line is required. Each button on the door station can control one or more switching modules with freely assignable configurations. The modules fit easily into existing flush-mounted boxes, for example. Communication and switching via mobile phone: Suppose you are briefly out for an errand: If the door call is redirected to your mobile phone, you can inform the person at your doorstep during the door conversation that you will be home shortly, or explain to the postman where to leave the package. If it’s a family member who has forgotten their key, you can even open the door, turn on the light, or control another switching task via the connected a/b switching modules using your mobile phone.