Scientists in Germany have demonstrated a startling new form of surveillance: identifying people using nothing more than ordinary WiFi signals. By analyzing how radio waves bounce around a room, researchers can effectively “see” and recognize individuals — even if they are not carrying a device and even if their phone is turned off.
Despite what others have said. It could in theory. But could it work with ordinary cell towers today, probably not. I base this on the accuracy of current location tracking by cell towers. They still use triangulation from my understanding, and aren’t highly accurate at that. The space your phone could be in is large enough for many people to be. So the granularity just isn’t there.
This is probably because of the large range they cover compared to the power levels they use. But in theory if the density of towers were higher, and the power levels were increased, they could probably do it in at least some locations with the perfect conditions.
There is another potential issue, which is the frequency. The lower the frequency, the less it will interact with an obstacle including people.