We all know the world's going to end at some point, and 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 mould. 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]