As DARPA puts it in its paper: "The need to be able to operate effectively in areas where GPS is inaccessible, unreliable or potentially denied by adversaries has created a demand for alternative precision timing and navigation capabilities." It's also working on self-calibrating gyroscopes and accelerometers and clocks that that will be able to track your position without relying on a wireless signal or other external sources: if your smart watch of the future knows where you start, and you move 350 meters north-west, for example, it'll know where you are without having to double-check with the internet, or a satellite.

Perhaps even cooler, researchers are crafting sensors that pick up "signals of opportunity" such as television, radio and apparently even lightning, to assist in location tracking. It's called ASPN (All Source Positioning and Navigation) and will particularly help in dense jungles (concrete or tropical) where GPS signals can often be obfuscated. This would also reduce power consumption for navi devices -- apparently one of DARPA's broad aims for the technology.