It's one of those "I heard a news story about this thing ages ago but can't find it on the internet"
Number of teenage ne'erdowells assembling in wotcouldonlybedescribedas a threatening-looking group on part of estate, much to annoyance of older residents.
Boffin comes up with the idea of blaring a high frequency sound, audible only to those of more tender years (your range of audible frequencies decreases with age)
Tykes steer clear
very sneaky, if very duffer.