[gruez]

I feel like this is the TV detector van[1] equivalent of cell phone companies. It might be possible to implement, but I doubt it's widely implemented as the article suggests, if at all.

[1] https://en.wikipedia.org/wiki/TV_detector_van

[Fnoord]

On the bottom of that article, this one [1] got referenced.

[1] https://en.wikipedia.org/wiki/Operation_RAFTER