Several young students have caught on to a recent trend: a ring tone that only they can hear and most adults can't. Dubbed the Mosquito, the noise stems from an antitheft technique in the United Kingdom, where it was used to deter youth crimes such as shoplifting. The idea is that most adults lose the ability to hear high-pitched sounds as they grow older, so this tone will reach the ears of only the young. Some enterprising unknown must have then copied this high-pitched tone and made it into a ring tone, which was then distributed to students in the United Kingdom and spread around on the Internet until it eventually reached U.S. shores. Teenagers who have downloaded the ring tone could then send and receive text messages and hear alerts without the knowledge of most, if not all, their school teachers.
But beware: Many adults may still have the ability to hear the tone--I know I could. You can click this link to see if you too can hear this alarmingly high-pitched sound.
Source: CNET News.com