This is a small 12mm round speaker that operates around the audible 2kHz range. You can use these speakers to create simple music or user interfaces.

This is not a true piezoelectric speaker but behaves similarly. Instead of a piezoelectric crystal that vibrates with an electric current, this tiny speaker uses an electromagnet to drive a thin metal sheet. That means you need to use some form of alternating current to get sound. The good news is that this speaker is tuned to respond best with a square wave (e.g. from a microcontroller).