I think is "passive" in the same way that a tick works, simply absorbing specific RF without radiating in a way that can be detected - sure a tick leaves a little hole but mostly you don't notice it at the instant that it bites, you just suffer afterwards. So you could have a situation where one manufacturers phone works but everyone else nearby has crappy reception.
But maybe this is an opportunity to make an "RF eliminator" to sell to people who think that they are RF sensitive.
Biting the hand that feeds IT
