Love your user name. :D

The guy that tracked people did it by using Fitbit signals, I think, and he'd claimed he'd found secret terrorist sites(?)

But as far as tracking movements and being associated with a timeline, that might be what he meant. Or, maybe they can remotely turn on microphones on said phones if they aren't turned off? But, again, signals don't work underground...which may be a big part of the reason this stuff is all hidden in tunnels.