I see the same problem here as with self winding watches -- the idea works well enough so long as a person has only one watch which they wear daily. Otherwise,

I see the same problem here as with self winding watches -- the idea works well enough so long as a person has only one watch which they wear daily. Otherwise, the watch may lose enough energy that it stops keeping time and has to be reset the next time it's worn. Watch collectors can buy "watch winders", a motor driven storage case that will keep their self-winding watches going when they're not being worn. I suppose that now the manufacturers will have to add little heating pads to keep these body heat powered watches going as well.