WALES: Pupils use ringtone teachers can't hear.
Techno-savvy school kids are getting away with using mobile phones in class by creating ringtones adults cannot hear.
British firm Compound Security was praised by the police for its Mosquito device developed to stop teenage gangs hanging around outside shops.
Once installed on a building it emits a high-pitched sound like a constant insect buzzing to drive the problem away.
It is highly effective because it cannot be heard by most people over the age of 20 but is deeply irritating to teenagers.
Now the youngsters have turned the tables by making high-pitched recordings which allow them to exchange text messages in class unheard.
Known as "Teen Buzz" it is spread from phone to phone via text message and blue tooth technology.
Howard Stapleton, MD of Merthyr Tydfil-based Compound Security, said he was "amazed" by the children's creativity.
He said: "This is the result of an astute teenager with a laptop."
Martin Moore is one of many Llanbedr residents who find the constant high-pitched noise from the nearby sewage plant unbearable Picture: ROBERT PARRY JONES