Small nine volt heater. Stop at step three for the case and the battery clip.
Step 1: Tools And Supplies
Ni chrome wire or thick steel wool type thing, different thicknesses and lengths heat differently. Some wire will need more voltage to glow red hot.
9 volt battery w/ metal case
Some kind of adhesive
Flat head screwdriver
Step 2: Dissecting The Battery
Use your screwdriver to pry open the top of the battery. Inside the battery are 6 AAAA cells (you need everything but these and the bottom cover).
Step 3: Creating The Heating Element
Cut about 1" of whichever wire you are using and solder both ends onto the contacts on the backside of the top cover of the battery (the picture explains it better). You can also stop here and solder wires onto the contacts to use it as a battery clip and use the case for whatever you like.
Step 4: Install Heater Into Case
Apply your adhesive to the BOTTOM of the battery case and slide in the heating element. Try not to let the wire touch the side of the case. Wait for the adhesive to dry.
Step 5: Finishing Touches
I used the utility knife to poke holes in the side of the case.
Step 6: Testing
To test your hand warmer hook up a fresh 9 volt battery to the leads on the hand warmer. If it works then the wire inside should glow orange. DO NOT LEAVE THE BATTERY ATTACHED TO THE HEATER!!!, by doing that you are shorting out the battery and the battery will begin to heat up. To use your hand warmer attach the battery in pulses until your hand warmer is at desired temperature. If your hand warmer works than it is because the wire is resisting the flow of electricity and giving off heat as a bi product. I am proud to say that this instructable was created using recycled materials! Please do not actually TOUCH the hand warmer while it is hot. This is made so that you can use it as a small stove or warm your hands OVER it. I do not recommend sticking hot metal down your gloves.