Oh god, I've only come across one but it was just horrendous. I frequently chase frequencies (I had to leave a meeting once because the burglar alarm system was so painful on my ears) and turn things off at the wall because of the noise. The problem is, all my friends are over 20 and can't hear it. I am too, but I can. They don't believe me when I say there's one installed, and I have no idea what they look like so can't point them out (is there a physical thing on the building, or is it just wired in?). I hate them so much. So, so, so much... it's such an infringement on the rights of so many people, I can't believe they're legal!! It's abusing children, babies, sensitive hearing people, autistics, various others - horrific. Ban them all.
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We are a fever, we are a fever, we ain't born typical...