Has working in a shop caused hearing loss?
Here's a quick way to test your hearing vs. your age.
They are ultrasonic ring tones. Kids are using them so that their teachers and parents can't hear their cell phones ringing.
They are grouped by age. Unfortunately I can't hear too good. If you don't think there's any sound on the younger ages (higher frequencies) just crank it up and see if a kid can hear it. If you have the volume turned up loud enough it will make them yelp in pain. Meanwhile, I can't hear it at all.