This is one ringtone you've gotta hear

Enterprising teenagers have hijacked a high-pitched electronic blip which adults cannot hear and turned it into a stealth ringtone.

It is suitable for use in situations where grown ups aren't meant know there's an incoming call or text message.

The ringtone - which can be downloaded from the internet - is proving especially popular amongst school students in the US and UK who use it in classrooms.

With it, students can receive text message alerts on their mobile phones without the teacher knowing.

As people age, many develop what's known as presbycusis or aging ear - a loss of the ability to hear higher-frequency sounds.

The ringtone is a spin-off of technology that was originally meant to repel teenagers - not help them.

Last year, a Welsh security company developed the 17-kilohertz buzz to help shopkeepers disperse youngsters loitering in front of their stores.

Mr Howard Stapleton, the inventor of the "Mosquito", claims the high-frequency pulsing sound can be heard by most people younger than 20 and almost no one older than 30.

Realising the commercial possibilities in the unintended use of the blip, Mr Stapleton's company has quickly produced it's own official version of the ringtone which they are calling the "the authentic Mosquito ring tone".