Paul__B:
Yeah, well I was just answering the question "buzzer that sounds with wrong polarity?".
I'm not faulting anyone for answering the question that was asked, I'm just suggesting that taping a battery-powered smoke detector to the board might be one approach to making a buzzer sound when the wrong polarity is applied. Further, if a smoke detector is a plausible answer to an electronics design question, perhaps it is time to reconsider the system requirements.