You may have heard about the “mosquito ringtone”. It’s a high frequency sound that only teenagers can hear. Some kids are putting these on their cell phones as ringtones so they can hear them, but teachers can’t.
Guess that as we age, we are no longer able to hear high-pitched frequencies. I didn’t want to believe it but I did find a site that had the pitches you can play to see how high you can hear. I was able to hear the 12khz one but nothing higher.
I’m thinking this has other applications. Maybe it’s a way of finding out how someone is without having to ask their age. Just play the different tones and look for the reaction!