Clicking the link below will produce a tone that is generally only heard by people under the age of 25. It has been used as a deterrent device to keep teenagers from loitering in malls and shops, and sounds similar to a buzzing mosquito. Typically the longer you listen to it, the more annoying it gets.
Can you hear it? I'd like to see if the cutoff is around 25 like it claims. Please comment whether you can hear it and whether you are older than, younger than, or exactly 25.