Have you ever considered a bell that buzzes or tone-chimes, like Westminster tones, to see if it doesnt set him off? We have a clock that quarter chimes, and does a full Westmister on the hour, and none of the dogs have ever reacted to it,even after an earthquake 'wound' the thing with pendulum sway. Seen some doorbells with changeable or WM chimes. Something about a doorbell.. I was watching a TV show where they kept ringing an apartment door, and after the 1/2 dozenth time that the dog with me jumped up, I was seriously considering changing the show just for some quiet enjoyment.