I think the question is the maximum possible range. If it requires something that's a few centimeters (or less) away from the skull, then a government would eit

I think the question is the maximum possible range. If it requires something that's a few centimeters (or less) away from the skull, then a government would either have to force you / make you agree to a scan, or would have to tap data generated by existing consumer devices (like they currently often do with phones/computers). Is it theoretically plausible that this activity could be read from many feet away, or further?