Comment by wkat4242
True but so can explosives. Clearly they were not competent.
Radio signals can be detected of course but it's possible to mitigate that a lot by only doing that at specific times and locations, or on request. And send the data out in batch. Ideally while you have the subject under observation so you know they're not monitoring for signals.
The same way Volkswagen hid their engine manipulation from tests by recognising the test and adjusting parameters.
Well, slightly off topic, but in the case of Volkswagen, everybody knew they (and other car companies) were doing it for at least a decade before the scandal blew up : car magazines were even publishing articles about it !