No doubt you have, on occasion, noticed teenagers congregating (some would say loitering) in shopping malls, outside of movie theaters or convenience stores, or in parking lots. In 2005, after his 17-yr old daughter was bullied and harassed by a gang of teens outside a local convenience store, a man in Wales named Howard Stapleton came up with an idea to solve the problem. He invented a device emitting a high frequency that could be mounted outside the shop. The sound would be so annoying to teenagers that they would leave rather than congregate outside.
The sound was at a frequency of 17 kHz, which teens could hear, but adults could not because most people lose the ability to hear higher frequencies after their early 20s. So because adults could not hear the sound, they would do their shopping in peace. Teenagers who came to buy something would shop and leave, rather than submit themselves to the obnoxious sound by congregating outside. Nicknamed the Mosquito, the device has been sold throughout Europe and in the US, has been praised and promoted by many police departments, but is also in the crosshairs of several civil rights organizations.*