When I was a kid, I could hear thing as high as 30khz very loudly (I was a medical journal kid). When I went into stores, the motion detector alarms would be horribly painful and adults would rarely pay any attention to me because they couldn't hear what was hurting me. Fortunately, my father was an audiologist and understood my issue. That was before he ran away and joined the circus, but that' another story.
When I walked through my neighborhood in the early evening, I could tell which houses were watching TV because the flyback transformers emitted a very loud (to me) shrill tone around 20K. Different flybacks produced different frequencies and I even knew which houses had more than one television (gasp!). Of course, I had no idea what a flyback transformer was at that time. All I knew was that TVs made a nasty sound when they were on.
My 15 year old daughter came to me yesterday to test her "school ring" the high pitched tone that kids use on their cell phones so teachers won't hear them ring. She handed me the phone and said "Can you hear this?" Nothing. *sigh*
My super human hearing has been replaced by Tinniitis.