I've always been very annoyed by those regular single beeps that smoke detectors start doing increasingly often as the batteries start to run out, to warn the user to replace the batteries.
Lately, I've been observing how a bunch of kids seem to sit in a room and just ignore those beeps completely, even after I point it out and ask them to really listen. They can't hear them. I seriously believe that they just don't physically hear them. Kind of like those dog whistles.
Is this backed up by science? Do kids under a certain age literally not hear those "low battery" warning beeps? Is this maybe per design, even? If so, why? Isn't it important that as many humans as possible hear this so that they replace the old batteries with new ASAP?
It's really frustrating to me when they don't even hear it, but I hear it very well.
I already asked this question a few days ago in "Biology", but it was "off-topic".