There we are! I knew the solution would be apparent once the collective brain cells of ECN got on the case! Bravo!
The idea for that was actually from an anecdote my late father once told me about how as a kid he decided that a conventional alarm clock wasn't loud enough, so he rigged up some sort of contacts on the clock to energize just such a large fire bell.
Apparently it was very effective -- Too effective, in fact. This was in the one of those Stoke Newington streets of small houses all joined together, and it woke up not only the entire family but also everybody in the adjoining houses as well. I gather it only ever got used on that one morning!