Well, this all is over-complicated for a person who probably even does not own an oscilloscope.
As a rough hack, I'd try some reasonable sensitive opto-TRIAC like Sharp S102S01 or S202S01 and just connect it's LED input in series with some suitable current-limiting resistor say, 330 Ohms by luck across the buzzer, be it piezo or electromagnetic. If this does not fire, reverse the polarity. TRIAC output could drive high voltage halogen or HF halogen supply directly, I'd be a bit cautious with magnetic 12V transformer, but probably still OK.