So maybe it's not BT, that was only an example theory. It also doesn't need to be always running, so could be harder to track. What if it turns out it's just some high pitch inaudible sound using morse code... I could go on but I'm not trying to crack the case - my point is that things like this that you assert don't exist, often do to turn out to exist on a long enough timescale. I remember reading a lot of tin foil hat theories on various things that some people asserted were illegal or simply impossible; then a decade later Snowden proved the theories right. It seems like these things happen regularly these days.