I have not purchased this particular brand, but I have had hot packs based on the same technology and they are worth owning just to amaze yourself and your friends with the cool way they work. Click a metal disk inside the pack and they heat right up. After they get cold, boil them to put the energy back into the system and they will store until you need heat again.

A Hot Pack yields almost an hour of steady, finger-reviving warmth once activated. Or if you're not too keen on showing the cold getting to you, just leave it in a pocket close to your body for a blast of secret, relatively-high temperature pleasure.

Much better than the traditional hot water bottles. I would totally get one if I was staying in NYC in winter. Resolution would be to visit NYC more this year! (via esh)