Can I supply a 12V buzzer with 18V?

I'm trying to make a little buzzer for my bike to sound occasionally to warn off bears. I have a 12V buzzer from Radio Shack (Cat. No. 273-065) and was wondering if I could run it off of 18V directly (2x9V Transistor Batteries series) for 1-2 second bursts, or if I should run through a lm317 which I worry might use more energy than the protection it provides. Are piezo elements relatively rugged when used like this?

Note: I can directly run the buzzer off 9V, with OK results, but I imagine 12V (or 18V) should be much louder.

Thanks!