A high-frequency sonic alarm created to stop troublesome teens from loitering in retail areas has been repurposed as a dance track and a mobile phone ringtone:
Merthyr Tydfil-based Compound Security released the "Mosquito" ringtone as a way of letting teenagers hear their phones ringing without adults knowing. It was developed because adults lose the ability to hear high-pitched sound.
But now the sound is being used in a dance track, Buzzin', with secret melodies only young ears can hear. The tune was developed after the success of the company's ringtone which was released in June. (…)
A condition called presbycusis, or ageing ear, means that by the time most people reach the age of 25, they cannot hear much above a frequency of 13 or 14 kilohertz.
Link (thanks, Nick)