The Chronos system from MIT is capable of determining the location of a WiFi device down to several tens of centimeters, without requiring addition sensors, and from that decide whether to grant a device access to the WiFi network or not. Safer drones, smarter houses and password-free WiFi access are within reach, if we are to believe MIT's Computer Science and Artificial Intelligence Laboratory.
Using the Chronos technology, a drone can, by keeping track of the occupants of the house (each with a WiFi device in their pocket) maintain a safe distance from them. Whoever has flown a quadrocopter (indoors), will agree that this is not a bad idea! In a two-room apartment with four occupants the system was correct 94% of the time in determining in which room there was an occupant. In a coffee shop demo, the system could determine correctly in 97% of the cases whether a person was inside or outside of the shop — a lucrative solution for small shops to prevent the 'stealing' of their WiFi.
The distance is determined by measuring the time it takes for the signal to travel from the user to the access point. The unique feature of this system is that only one access point is necessary in order to determine the location.
More information: https://news.mit.edu/2016/wireless-tech-means-safer-drones-smarter-homes-password-free-wifi-0331.