A while back I wrote a post on how shopkeepers in the UK were using a device that continuously emits a high-frequency whine to deter youths from loitering near their business, while being inaudible to older adults. Someone on QT3 recently posted a link to a website that allows visitors to download and play something similar, so that you can hear for yourself if the sound is audible to you. It turns out that despite being 33 years old, both my wife and I could hear this sound, and, yes, both of us find it extremely unpleasant and annoying.

Someone else then posted that students in the UK were using similar sounds as the ringtone of their mobile phones, allowing them to ring in class while being inaudible to their teachers. I can only imagine the barely suppressed glee in the classroom as all the students are able to plainly hear something that the teacher can’t notice at all. You can download these ringtones here and see at what frequency your ability to hear the sound stops. Both my wife and I could hear only up to the 15 kHz version which is consistent with the website’s claim that it can only be heard by those aged 40 years and below.

Try it for yourself and let me know your results.