>this would make the Piezo very sensitive to vibration -ergo
>when rain falls on it vibration happens voltage occurs. I
>think I've seen water proof Piezo tweeters somewhere so they
>might work.

I was not thinking of having it like that, I was figuring on having the
piezo unit driven at low level by being the tuned element in an oscillator,
and a PLL to look for frequency shift, or some form of amplitude detection
to look for amplitude damping. It may be that if the level of oscillation is
controlled at a low enough level, then a drop of rain may be enough to make
the piezo element go low enough in Q, or be damped enough to cause it to
drop out of oscillation.

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