I'm almost done with my latest build, "The Freak" (pics forthcoming) and I went to RS to get one of my usual piezo elements.  They were out.     So, I picked up a "piezo buzzer" with the little circuit board soldered to the hot element.
No problem, I thought; I cut the little wires and soldered my hot lead to one of the little solder blobs left over from the circuit board.

Tap-test was fine.   Stuck it in the box and waited for the glue to dry.    No sound.    Fortunately, I hadn't glued the lid....
Popped the strings off and took a look; the hot lead had pulled off completely.   Further, when I tried to re-solder it wouldn't stick at all.  Seems there's a thin layer of some sort of conductive material on these and it must be very fragile.
RS says they'll get in my regular piezos tomorrow.

Also... I took a rather large piezo out of a smoke detector.  This is about 1 1/4" in diameter.  the backing appears to be stainless steel.  These are not soldered; the connections in the smoke detector are springs.

Anyway, I tried to solder one of these up and could not get the solder to stick at all.  Even roughed up the surface by scraping....Nothing.

Anybody ever use one of these?