These devices have been a bit disappointing. We ordered a set of these as a gift. When they were first removed from the box, only one would activate. The one active device performed very well, but we could not get the second device to activate. We notified Bits and Pieces, and within 24 hours a replacement set was on its way, so I have to give them BIG compliments for customer service. However, the second set of devices had the same problem - only one of the two hand warmers actually worked. With the two sets, we now have one pair that works most of the time, and one pair of useless devices that have never been able to activate. With a 50% failure rate, I can't say that these are a great product, but I am happy with Bits and Pieces reaction to our issue.

These kept warm about a half hour and then became hard , stiff and uncomfortable in my mittens. They also needed to be clicked at least a half dozen times to activate. Boiling them 5-10 minutes after each use will be a pain. It would be better to buy disposable ones.