For about $250, you can make your very own space-age spy tech, following an MIT professor's instructions.

It can capture high-resolution images of small objects -- like a message written in push pins that had been hidden behind a foam plate.

Using a garage-door opener, microwave parts and a cordless drill, Gregory Charvat made a working synthetic aperture radar (SAR) system, the same kind of technology the military and NASA use. Charvat used algorithms to combine the back-scattered radar images into a high-res photos of things in his garage, like a Cannondale bike and a model F-14.

SAR is useful because it combines multiple radar images to create higher-resolution images than would otherwise be possible. There are a couple ways to do it -- by using a single antenna on a moving object, like an airplane or spacecraft, or by using multiple small antennae scattered over a large area. NASA uses SAR to create detailed maps of other planets, and it can be used to map the spread of oil in the Gulf of Mexico, for instance.