I use reusable hand warmers when I work at home. For instance, when I am going through a typical day, especially during winter, I am typing for hours on the computer. This keeps my fingers in motion so I get to enjoy that they do not get affected by the cold. I have heating but there are times, especially as the day gets later when I just need a little warmth for my hands.
I use two different types of hand warmers. One is the type that comes with a chemical in a clear rectangular pouch. It looks a little like an ice pack only you just touch it and the chemicals inside heat up.
How long the heat lasts depends on a number of factors such as the size of the product, how insulated it is, and how the hand warmer is used. Expect anywhere from half an hour to two hours plus of noticeable heat.
Microwaveable Hand Warmers
The other ones I have are hand made and they are called corn warmers. You put them in the microwave and boy, do they warm your hands up! They are my favorite because they are going to last a lot longer than the chemical variety.
There are only so many uses you can get from them, but with the homemade cotton-cloth variety you get a lot more use out of them because there are no chemicals inside to go bad eventually.