The street finds its own use for technology, said William Gibson, not realising that this sort of talk leads to bad TV shows. However, it is true. One fine example is the way children have taken a weapon aimed at controlling them - a near-ultrasonic tone inaudible to adults that, fed through a PA, drives them out of an area - and adapted it to a stealth ringtone that lets them communicate without alerting the straights. .
Just about all people past the age of 20 start to experience a drop-off of high frequency sensitivity as hair cells in the ear die, meaning that there are parts of the audio spectrum left for the sole use of annoying teenagers. Thus, they can carry on texting each other in peace and quiet at the back of the classroom without pedagogical interference, safe in the knowledge that even if they are discovered, the implicit insult to the aged gives them virtual victory anyway.
It’s just the start of an arms race, though. It would only take a minor tweak to a bat detector to make it go off in the presence of just such an inaudible ring tone. After that, a smart detector could work out the frequency of a second ultrasonic tone to mix with the first, creating a beat frequency modulated with Max Bygraves in the head of the accursed child. Total Spectrum Dominance, as the US war machine has it, will be ours.
In any case, time is running out for the whippersnappers. To my great delight, progress is being made in discovering why the cilia in the ear don’t grow back - and blocking the gene that creates the protein that blocks the regrowth. I can once again hope to sit in the gloom of crepuscular woods and hear the bats swoop overhead, something I haven’t been able to do since I was in my early twenties. That’s if they aren’t blocked out by the blasted ring-tones.