I'm sorry that this is a 'non-answer' but I think that you seem to be seeking something that can't possibly exist. The laws of physics state that you can't create energy. Hand warmers convert chemical energy to heat energy. That chemical energy either comes from batteries (which then need to be replaced after giving up their energy) or from a direct chemical reaction (which either can't be reversed or, if it can, would require far more than a simple 'click' to provide the necessary amount of energy- e.g. you'd need to boil the hand warmers first).
This isn't exactly what you've asked for but it might still be of interest:
http://www.thehotrox.co.uk/
Chris