In Sloan Review:
" ... If WiFi can find you — instead of you trying to locate a signal for it — the result could be smarter homes, more efficient businesses, and password-free WiFi. According to researchers at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL), it could also make drones safer by helping them avoid specific locations (including their operators) accurately, or help find lost devices with uber-accurate tracking. It could even enable you to find friends and family members in, for example, a train station or museum in countries where WiFi is not as prevalent as in the U.S., without the need to connect to a WiFi infrastructure.
Developed by a team led by Professor Dina Katabi, the new “wireless localization” technology, called Chronos, operates somewhat like sonar and radar, but with far greater precision. It locates users by calculating the time that it takes for data to travel from one device to another (for example, a cell phone and a wireless router). ... "