Piezo demonstration II
Piezoelectric generation of electricity

When you bend or flick a piezo electric crystal / transducer the force (and change in force) creates a voltage pulse across the crystal. The voltage can be surprisingly large ca. 50V but the current is small (10-100 uA) and of short duration, so the average overall power is very small. The piezo element is often attached to a larger thin brass disc forming one connection to the thin piezoelectric crystal while a silver pad on the other side forms the second connection. These two connections, to each side of the element, allow a good electrical connection to be made. The connections are fragile and if you try bending the device with your hands you can easily break both the connections and crystal. This 3D printed jig holds and secures the piezo element to safe guard from breakage and means you dont need solder connections which are fragile.

I have a MKI piezo 3D printed demo which is deigned for wire ended piezo discs - see (simple piezo demo click here).
The MKII version shown here is even simper, it securely holds the piezo disc to the LED and no soldering is required.

LED indicator
The two wires of the transducer go to a LED. The open circuit voltage pulse may be high but the LED loads the piezo transducer and seems to limit the voltage so it lights the LED. Each time the piezo is flicked the LED will flash. As the voltage created by the piezo is an AC signal you dont have to worry about correct polarity connection of the LED - it will work both ways.

Parts
If you are buying the parts on-line almost any large piezo disc will do (i.e. ca. 50 mm diameter) and search for hyper bright LED (try red or yellow as they are bright but blue or white may take too much power to light properly).