Coffee tins - great for string-based telephone construction, improvised percussion and, finally, for keeping things in. However, as it turns out they're good for another thing as well - cobbling together a radar system. We can see how this would be useful when we find ourselves against the wall when the zombies apocalypse comes.
Now, while the tins take up a significant part of the construction, there is a little more to this. This device is based on a design by MIT for a radar that is capable of range, Doppler and Synthetic Aperture imaging. The creator of the above system, Timur Balbekov, used a Cypress System on a Chip microcontroller to spit out Doppler readings in real time.
If you too wish to acquire vital technical survival skills that may or may not help you survive the inevitable onslaught of the undead, you can get all the details on how to build the rader from MIT's website here.
