A bare piezoelectric transducer that can be used either as a sensor, or as a speaker.
Good to have a few of these around.
A handy component for all kinds of projects, as they can both produce sound and revive it. Not that all speakers and mics cant, but as far as cheep components go they are rather versatile.
I ordered batteries and a set of test leads. I received them within three days of when I ordered them and I got a great price. Fast service and a great price - what more could you want.