Looking for Piezo Voltage Warning Schematic

[Jeff]

Hello all.

I am in search for a small simple (as in quantity of parts used and
availability) low voltage warning piezo buzzer schematic.

If you could provide one that would make a piezo buzzer "buzz" when voltage
is too high (a high point setting) as well as too low (a low voltage point
setting) that would be excellent.

I have searched the NG and used good ole "google" without too much success
at all. Any and all help would be greatly appreciated and I thank you in
advance.

Jeff