One might be wondering, how the switch module can fit into a standard switch plate. In our house we are using a model which provide a mounting frame for it. Therefore it's easy to mount everything into this frame. The pictures shows how I have it done. It contains two switch modules with eight buttons.
The boards and frames are fixed hot glue.
The switch plates are a little modified on the back to fit it into the system.
On the upper half shows a complete systems. On the lower half the switch plates are left for better look onto the frame. It can be seen that the switch plates are clipped into a frame.
The back view shows how flat everything fits into the cover. It is possible to mount it directly onto the wall with a small hole for the bus wires.
If there is a flush socket than it's possible to mount additional a relay module under the switch.