hmm... i think this is the anti mosquite tone that was deviced for mobile phones
it basically works like this: the phone will emit a sound so faint that you most likely wont be able to hear it but its very irritating for mosquitoes so they will avoid that area
though this is the first time i heard that teens are using it. the sound doesnt mean a thing
of course, you can make use of this by something like say regular intervals
example, multiple choice: a,b,c,d. if the answer is a, you play the tone for a certain amount of time, another time for b, another for c, etc etc