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A bit of steel wool held to a battery's contacts will create a short and start to spark, and if you're careful, you can direct that spark onto some pre-arranged tinder, starting a fire. Of course, this also works with a 9-volt battery, which I'm almost positive Les Stroud has used on Survivorman, but it's a nice idea to show it can be done with something we've all got in our pockets. [via MAKE]