you can start with a tens unit, or there are some programs you can use with your computer sound card, as I recall, and an audio isolation transformer (which you should be able to find either on the internet electronics surplus sites, or at an electronics supply store---start with an 8 ohm to 1 kohm transformer---necessary for electrical isolation). I believe there is a yahoo group or ten on e-stim, that has various reccomendations. It basically depends on how good a quality you want, and how much are you willing to pay for it. It also doesn;t work for everybody. This is what my research taught me, when I was curious about it.