Back to school - with the phone call your teacher can't hear

Students have always tried to best their teachers in the small-scale warfare that is school, and now they have biology and technology on their side - at least where mobile phones are concerned. The psycho ringtone has arrived in Austria.

Ringtone marketers are promoting products called "Teen Buzz" or "PsychoBuzz" to students, claiming that their teachers cannot hear them.

It makes slagging off that stupid maths teacher or exchanging notes during class ever easier and tempting. But what's behind the buzz?

The idea is based on the phenomenon presbycusis or the "ageing ear." It is a biological fact that people lose the facility to hear high frequency sounds with progressing age - starting around age 20.

Sounds in the range between 17 and 20 kilohertz - the highest frequencies humans can normally hear - can still be heard by teenagers, but not by older persons. Like teachers.

Most human communication takes place in the range between 200 and 8,000 hertz.

The ringtone business inverts a concept used in Britain, where the high-frequency so-called "Mosquito" sounds were used by shopkeepers to dispel loitering teenage gangs.

Security systems emitted a 17 kilohertz sound that proved highly annoying for teenagers, but left people over 30 completely unaffected. There are, however, exceptions to the rule.

Based on the same concept, teenagers can download those high- frequency ringtones on the mobile phones, alerting students to incoming calls, voicemail or text messages.

It is converted into MP3 files, and emailed along to others, played on PCs and mobile phones. Some providers even offer versions in different frequencies, in order to make sure that the buzz can be heard by the intended recipient after all.

But not all of them work as promised. A little road-test of several ringtones offered showed that some could indeed be heard by adults, although as a "very high, very uncomfortable noise," as one put it. Not inaudible, but annoying enough to grit one's teeth.

For teenage tester Daniela the idea was "cool", but she was not too sure if her teachers would not cotton on eventually. And anyway, having the Black Eyed Peas announcing an incoming text was more fun.

With most schools having rules in place banning the use of mobile phones in class - also to prevent cheating - students are one step ahead in the game.

Teachers will have to find new ways in the tech-game of beating their students' inaudible messaging. dpa im sc