Zenith has one that can be set up so that it won't fire at all. The cam is round. It has a notch that clicks when the shot would have gone off. Once you get comfortable with that you can move to the clicker cam that gives a click just before the shot fires. Then it has a third cam that is a pure backtension surprise release.
It also comes with a video that shows you how to put it together and a little about shooting back tension. The video is a start, but I needed a lot more help to learn to use back tension effectively.
http://www.zenitharchery.com/index.html
Joe, the owner is a great guy. He answered a couple of questions right away for me when I was just starting.
Good Luck,
Allen