OT: very high freq ring tone

["oryoki2000" oryoki2000]

Very off topic:

Schools forbid the use of cell phones in class, of course.  A clever
high school student found that his teachers have a difficult time
hearing very high frequency sound, while teens can still hear it.  So
the student created a cell phone ring tone using the high frequency,
and employed it to alert him when text messages arrive.

The student was inspired when he read a report about a British company
that markets a system to disperse teens who loiter around convenience
stores.  The sound is very annoying to teens, but inaudible to most
adults.

Now the tables are turned, and kids can use the cell phones in school
again, provided their teacher is over 30.

http://www.nytimes.com/2006/06/12/technology/12ring.html?hp&ex=3D1150084800=
&en=3D6e65a1e8bdeab1e1&ei=3D5094&partner=3Dhomepage