You're right, I wasn't clear. I want to use an off-the-shelf, store-bought button and a bell somewhere, and put the controller in between. When you push the button at the door, the signal will go to the arduino and there the program will decide what to do (for example, pass the signal to the bell).
I know how to program this and how to connect on a prototype board with a piezo and a regular button. However, I have no idea what such wiring should look like and what components I will need in a real installation, I would not want to damage anything/anyone or set fire to it.