In a television episode of Person of Interest last season, the plot revolved around an artificial intelligence known as "The Machine" using high-frequency tones to communicate secret messages to our younger heroine which was completely missed by the older antagonist.
Apparently the show transmitted real messages at very high frequencies, which I was unable to hear. The YouTube video embedded here pairs the rising pitch with a visual display of the current frequency and is an excellent way to determine the edges of your range of hearing
The basic principle is that as one ages, the tiny hairs in the inner ear lose some of their functionality, slowly causing hearing loss in the very high frequency ranges. Higher-frequency tones are sometimes used by teenagers for their cell phone ring tones. While cell phones are usually banned from the classroom, most teachers are old enough to have already experienced some hearing loss and can thus no longer hear these tones when that phone rings in class.
So the argument implies that the teacher won't know what's happening. Unless something radical has changed with human nature in the last few decades, however, only a senile teacher would not be able to make note of the grins and grimaces and glances of the other students when such a call comes in. And even senile instructors are likely to get occasional real-time reporting help from the class tattletales.
A couple of companies use this same principle to create wall- or pole-mounted anti-loitering devices. The transmitter can be placed wherever teen loitering is a reoccurring problem, the expectation being that most teens will find the tone so annoying that they’ll go somewhere else. Adults, on the other hand, aren't bothered by the tone because they can’t hear it any more.
Have you ever found yourself trying to buy a meal at a fast-food restaurant when school lets out? Have you ever tried to get a group of teens to shut up and stop texting during a movie? Have you ever had to repeatedly shout at some kids to get off your lawn?
No more! Soon you'll be able to say,"There's an app for that!" Just launch the shaking fist icon, turn your volume to max and watch those young whippersnappers scream and cover their ears, then run far away as fast as they can!
This will surely be the #1 bestselling app for people over 25!
I just have one minor legal question before I launch my Wall Street empire: Can an officer of the law charge you with disturbing the peace if he's too old to hear the tone?
This was certainly fun. I could hear a sound from 52 Hz up to about 17400 Hz (speakers on 10%). So is there a scale for what's normal? I am a 52 yo teacher and I now and then feel that I am having hearing problems.