This article talks about a high pitched sound that is irritating to youths, but to which adults are oblivious. They're supposedly using it to keep teens away from their stores, where large groups of teens had been congregating.
If it's true, wouldn't it keep anyone with kids away from their stores? And anecdotally, it seems to be hearable by anyone who has protected their hearing over the years (unlike me, damn my stupid younger self). I'll have to check this one out on the girl. I can hear a tiny amount of high pitched rhythm. But I wouldn't have noticed it if I didn't already know it was there.
If you'd like to check it out, go to the link at the bottom of this article. Leave a comment to let me know what you hear!
at 8:59 AM