This is a very good, simple circuit.

It would easily fit into an Altoids tin.

Many years ago, a friend and I bought a half dozen microwave oven 
beepers at a hamfest for a dollar.

I used one of them in just a continuity circuit. That is the beeper, a 
9 volt battery, and clip leads that are part of the negative lead going 
to the battery.

I never thought about the switch option Butch described.

I may just have to make that modification.

-- 
Mike Duke, K5XU