I am officially old.
The Brits have been using a high-pitched "mosquito" sound that only teenagers can hear to drive loitering adolescents away from businesses where they're not wanted. (Age-related hearing loss starts at age 20 or so; high-pitched sounds go first.)
The teens have struck back, copying the sound to mp3 format and using it as a ringtone. Now they can get calls and text messages without alerting teachers or other adults.
Can you hear the sound? Two versions of it can be found here and here. I cannot. (h/t)