The hearing section of Chapter 5 in Lilienfeld mentioned that as we age our ability to hear higher pitches decreases. According to an article in the New York Times, a group of British store owners used this idea to prevent teenagers from loitering by playing a screeching sound only the teens could hear. However, the teens took this idea and turned it around to create a ringtone that students couldn't hear but parents and teachers could not.
The article had an mp3 attachment of the sound for readers to test their own hearing. After learning that I could hear what sounded like a screeching microphone or nails on a chalkboard, I decided to test this idea on the rest of my family. I turned out my sister could hear it, but our parents could not. My sister and I are both in our 20s and our parents in their 50s. The article mentioned a cutoff age of around 30 years. Because 4 people is a very small sample size, I found a downloadable file of the sound and sent it out to my entire contact list for my personal email, as well as Professor Briggs, explaining that I was doing a study for my Psychology class and just to let me know if they heard this sound. In order to prevent demand characteristics or possible lying, I asked them to also tell me what they heard.
Including the 4 people in my family, there were a total of 25 responses. It turned out that everyone under 45 could hear the noise. Additionally, my 63 year old aunt could hear the noise. The results showed a negative correlation (r = - .7896) between age and ability to hear at that high of a frequency. This means that as a person gets older their ability to hear higher frequencies worsens. However, this is a correlational study, so we cannot determine a cause and effect relationship. Furthermore, a sample size of 25 may not be large enough to prevent outliers from skewing the results.
Here is a link to the article: http://www.nytimes.com/2006/06/12/technology/12ring.html