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.htmNow this one looks pretty simple and might work…..
http://www.reconnsworld.com/audio_electretamp.htmlThe op amp stuff gives me ideas…
http://www.redcircuits.com//Page28.htmSeems like a cool chip but would probably never figure out how to set it up…
http://www.rohm.com/products/databook/audio/pdf/ba3430s.pdfThe 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