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:
Jonathan, The piezo in the card will be used as a speaker. It should be a small flat metal (brass usually) disc with a spot of ceramic like stuff in the middle, also flat. a wire should be attached to the metal and to the ceramic. This is the piezo and you wire this to a 1/4 inch jack and then plug into and amp and voila you have a pickup.
I have found a lot of them in old phones, has to be the phones that are really heavy, piezo is the ringer between two metal plates, cant be a digital phone. Also window alarms at the dollar store for 99 cents. Happy Hunting. PS you can find these old phones at Goodwill, Salvation Army, ect...
I find a lot of sources for piezos by searching through yard sales. A lot of times, noise-making toys, etc, are available for next to nothing (my kind of price). Some have small speakers, but these can be used as pickups, too, but you may want to build a pre-amp to up the signal.