Weird question I know, but mine is rubbish so I'm on the lookout for a decent one.
I bought a Byron pack which had the push unit, 1 plug in chime and one battery chime I'd planned to have the plugin one somewhere central and the other one as a roamer (out in the garden or garage etc.). Set it all up as recommended and it is just unreliable. Sometimes 1 of the chimes goes, sometimes nothing. I'd say it worked for 60% of the time, but got gradually worse. In the end I took the bell off as at least if there is no bell people knock!
Knocking has its limits though so am thinking of trying another system. Any decent ones out there?