The sounder for my doorbell plugs into a mains socket, which gets rid of part of the battery problem. However, because it is not near the front door, and additionally the sound is produced when the push is released, callers almost always knock as well.
Somebody recently remarked that it wasn't working, and I demonstrated their error, commenting to them that I thought the point was to put it where _I_ could hear it. The indicator light flashes, but is clearly not trusted.
Chris