About 20 years ago you could buy small paper packets of hazardous chemicals, which, when shaken vigorously, would start up a chemical reaction and stay hot for a few hours. Then you threw it in the bin. It was a Christmas morning novelty.
How technology has improved! Battery maker par excellence Eneloop (a part of Sanyo) has revealed its rechargeable pocket heater, a fashionable little white egg thing that gets warm on demand. Charge it up, and you can heat a small, round part of your body for five solid hours.
Not the most environmentally sound way to keep your hands and genitals warm this winter and more than a slight waste of electricity, but if you plug it in and charge it up at work it is at least a free source of heat for the cold winter evenings.