A cellphone ringtone that uses a constant, 14.4 kHz frequency generally only heard by people under 20. Also known as "Teen Buzz" or "Mozzy Tone," it became popular because parents and teachers usually cannot hear the high-pitched tone when the phones are ringing. After 20, most people's ability to hear these higher frequencies begins to decline; however, some aged 50 and older have been known to recognize the ringtone. Keep Teenagers From Loitering The Mosquitotone uses a constant 14.4 kHz sound; the idea taken from the modulated 17 kHz tone of the Mosquito sound-emitting device introduced in Wales in 2005 from Compound Security Systems (www.compoundsecurity.co.uk). The Mosquito was designed to prevent teenagers from loitering in the area. After a few minutes, the sound becomes very irritating, and the crowd tends to move to another venue. See ringtone.