I worked at a consulting company about a decade ago that designed an indoor tracking system. It could track a device to within a meter, and that was no trivial

I worked at a consulting company about a decade ago that designed an indoor tracking system. It could track a device to within a meter, and that was no trivial undertaking. I always have a laugh when I see some startup making a child tracker/pet tracker using iBeacon. You need a large array of radios to track the beacons, you have to model the physics of the building's construction (absorption, Rayleigh scattering, etc), account for multiple floors, and come up with a working algorithm that combines all the RSSI readings to produce a precise location.