As many of you may already know. Piezos can be made into a simple and effective contact pickup. Did you also know many can be found cheaply or even free? Here are a few places I found piezo elements free because they were going for the trash:
Cards that play music
some talking stuffed animals
I found 4 or 5 out of a broken rockband drumset
an old auto alarm system.
Hope this helps. Feel free to add to the list.