What is a high pitch noise that adults can't hear?

While many teenagers can hear sounds in the 16 kilohertz range or higher, most adults past the age of 25 cannot. For this reason, 17-kilohertz ring tones are popular among high school students who want to receive messages on their cell phones during classes where cell phones are forbidden.

The loss of high-frequency hearing is a natural result of aging. People over the age of 50 often have a hard time hearing pitches higher than 11 or 12 kilohertz. Noise generators that produce a loud 17-kilohertz whine have been used by retail store owners to discourage teenagers from loitering around their storefronts. While most teenagers find the noise unpleasant, most adults cannot hear it at all.