A crowd-control tone was repurposed into a ringtone adults cannot hear

Evidence

However, young people now benefit from this basic idea because it has now been used to provide mobile ringtones, sometimes known as “teen buzz,” that cannot be heard by older people. The original teen buzz was created by recording the output from a mosquito device, but nowadays there are plenty of synthesized downloadable teen buzz ringtones available online. In general, these ringtones are not audible to adults over 25 years of age, but this does depend on the overall amplitude of the sound and the rate of presbycusis change for given individuals. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2576

Categorization

• CANDY: Perfect elevator fact: kids use the anti-loitering tone as a ringtone so teachers can’t hear it.
• XREF: Reverses the mosquito’s purpose — same acoustic trick, opposite social function.
• BMF: Echoes the age-stratified hearing of the society in We by Zamyatin — a world where perception itself separates generations.