Just curious, why do most wired doorbells need a transformer, with the associated hassle of wiring from a mains source to the tranformer and then to the bell, when they could just as easily use a 9V battery in the sounder unit instead?

I presume there's a good reason, just I'm too much of a numpty to work it out for myself.

I know there are some battery only devices, but they are all horrible and don't meet SWMBO's audio requirements nor visual aesthetic requirements. And wiring something up doesn't meet my requirements. (And wireless ones are either crap, don't work in my house, look ugly or don't make the right sort of ring for SWMBO!).

Matt