In a more regular appliance, the current Valve Lighthouse VR-tracking system works by sweeping lasers very precisely across a room and using the timing differences across the sensors on the HMD to triangulate its position in the room.

There is a good talk by one of the engineers who worked on the initial prototypes, and IIRC they both require and are able to achieve something like nm accuracy when they sweep the rotating masses with the lasers on them (That is, not only is the frequency very precisely controlled, the phase cannot drift either). With the help of some custom components they can do that for a hundred bucks.

I'm slightly hesitant to go into it for mostly ethical reasons, but military technology has always fascinated me if purely because of the toys they get to play with. The amount of gear even a World War 2 aircraft had by the end of still surprises me, i.e. The Mosquito had a primitive version of what we would now call a HUD displaying a radar horizon and a gunsight. Know-how and an unlimited budget go a very long way.