I get the impressionthat the buttons get pressed too hard and it damages
the innards. Likely to happen when you can't hear the bell from the outside
- the courier just presses harder.

The button is the weak link.

I have a mains powered bell - I liked the idea of the illuminated bell push
.. However, the bulb has failed and I can't be arsed to fix it. Transformer
is in the Consumer Unit.