It's a coil (inductor) to generate flyback voltage. There's a switching circuit that creates a high voltage to apply across the piezo element. Piezo elements are generally designed to be run at high voltage; 30-200V is not uncommon. In a really good design the piezo will also be in a Helmholtz enclosure as well to really get everything from the system as a whole. Years ago I designed these things for car alarms. 120dB was on the low end of what you could achieve...
Do some searching on piezo elements; off the top of my head I'd say have a look at Murata. I seem to recall that they have some pretty good doc's on these things.
Mike Tripoli
P.S. I found the doc I was talking about pretty quickly: http://www.murata.com/catalog/p15e6.pdf. It's a good starting point...
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