Stores in England wanted to disperse teens but not bother wallet carrying adults. So,the developed a technology used a high frequency sound the adults couldn’t hear because of the againg process. An inventive teen took this one step further. He (she?) researched the sound and turned it into a ringtone that students/teens can hear and teachers/adults cannot.

More on the tone can be found in the NY Times if the bloody link works. . .

(yes!!! i can hear it!)