Of course, if you claim your wrist-puter or in-shoe gadget can cure cancer, or something like that, you'll need an FDA-approved classification reserved for medical devices, which need extensive testing and are much harder to obtain thanks to stricter regulations (as you'd expect.)
There is also the possibility the buyer would also require a prescription depending on the devices actual functionality. Granted that's typically reserved only for items the FDA feels can be abused or when they feel safety is an issue if used improperly.