This is interesting: an invention that is no more than a loudspeaker emitting a high-frequency sound that aparently people over 20 cannot hear. It is intended to make teenagers go away from non-loitering zones or whatever, which I feel is kinda "nazi" to me. Nowadays it's being used as a cell phone ringtone by kids, so that their parents and teachers cannot hear it. Now, I am 23, being 24 in a month, and I was able to hear it, although it is VERY irritating. Dogs should go crazy with this thing. Try to see if you can hear it, and if you want please post your age so we can see if it's true that older people cannot hear it.

The audio (mp3)

Please don't listen to it too loud, I am not sure if this is 100% safe, don't want anyone getting deaf here.