Israeli researchers have created the tiniest-ever optical gyroscopes, as small as a grain of sand, but still maintaining the keen accuracy of their counterparts hundreds of times larger. Optical gyroscopes are generally used for navigation in airplanes, ships and satellites, in which they track movement without reference to external navigation points, by measuring the vehicle’s rotation rate and linear acceleration. This is called inertial navigation. It’s extremely accurate but, up until now, only possible in gyroscopes and weighing two to three pounds.

They only need to set their position once, quickly, and then they can remember where they are for quite some time.

via Nano-Gyroscopes Will Let Cell Phones Navigate Indoors, Underground | Popular Science.