GPS is a fantastic technology, allowing you to pinpoint your location within a few feet anywhere in the world, except all those places where you can't get a clear view of the sky, like inside buildings. People spend rather a lot of time inside buildings, which is what makes this new geomagnetic location technology (which does work inside) so cool.
Every point on Earth has a unique geomagnetic signature, generated by the Earth itself and (more recently) things like buildings that have metal and electric wiring running through them all willy-nilly.
Detecting these geomagnetic signatures (or "anomalies," if you want to be excessively dramatic about it) can be done with a slightly-fancier-than-normal compass, just like the one you have in your smartphone. And once you correlate each geomagnetic anomaly with a specific position, you can use them to navigate anywhere with an accuracy of six feet or better. By "absolutely anywhere," we mean that this system works indoors, at the top of skyscrapers, or thousands of feet underground.
As cool as this system is, it's not going to supplant GPS anytime soon for the simple reason that you have to pre-map the anomalies in an area before you can use them to navigate. The company behind this tech, IndoorAtlas, provides an Android API and mapping tools that make it easy to do it yourself, and it's hoping that retail companies will use it to help shoppers navigate through their stores once they've downloaded the Indoor Atlas app, which you can watch in action in the video below.