Here’s some leading contenders…. in the I make it catagory

I like the idea of modifying the old lady’s clapper…

http://home.maine.rr.com/randylinscott/dec97.htm


Now this one looks pretty simple and might work…..

http://www.reconnsworld.com/audio_electretamp.html


The op amp stuff gives me ideas…

http://www.redcircuits.com//Page28.htm


Seems like a cool chip but would probably never figure out how to set it up…

http://www.rohm.com/products/databook/audio/pdf/ba3430s.pdf


The Schmitt trigger looks like it might work. Maybe hooked to a LM555 timer …..

http://www.swarthmore.edu/NatSci/echeeve1/Class/e72/E72L2/Lab2(OpAmp).html