We all know the world's going to end at some point, and sure, maybe it's not entirely "likely" to happen anytime soon—but better safe than sorry. So assuming you've already been working diligently on your underground, radiation-proof bunker, what's going to happen when you need extra keys made with nary a (non-zombie) locksmith in sight? Fortunately, as Hack A Day shows us, there's an easy, accurate enough way to make your very own spare keys with nothing more than some plaster, the sun, and a giant fresnel lens.
The first part is easy enough; simply put a thick layer of plaster of paris in a small box, place the key halfway into the surface, fill the rest of the way with plaster, and let dry for a few hours. Then, place a bowl of zinc pellets (which you can buy on the internet) beneath a fresnel lens to give you molten metal. The fresnel lens can capture the sun's oblique rays, making it more efficient as a concentrated energy source. Once the pellets have melted, you're then free to (carefully) pour into your key mold. Allow the zinc to cool and bam—you have yourself one fresh, slightly less sturdy, yet still functional key.
Of course, all this is dependent on the fairly bold assumption that you'll have a massive fresnel lens lying around should the need arise—so better add that to your End Times shopping list. And stay vigilant, friends. [Hack A Day]