BenzoThey do work well. But I had some time left over in them and as you know you can not turn them off. I made the mistake of having them in a hotel room for a bit. Walked outside and then back inside and was afraid of some air poisoning. I would not have noticed had I stayed indoors. Learned quick to leave them outside until the fuel runs dry. That's why I'm interested in these. But are they truly just a very warm battery that is being sold as a hand warmer?