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.
Awesome folks, huge stock and it's actually in stock (WAC), fast shipping. One of my few favorites for electronics and parts. A+ Solid.