Mob Peeve

This is definitely not the solution to answering calls at inappropriate times, but it may be a solution for younger people who suffer from having annoying ringtones or constantly forget to turn their phone to silent mode before class begins. Ultrasonic sounds are high frequency sounds, and studies have shown that it can generally only be heard by dogs and in younger people. Some claim this age threshold is around 20 ~25.

Go to http://www.ultrasonic-ringtones.com/

You can try out your ultrasonic hearing skills on 12 different tones and download them as ringtones.

The sounds may be different through a computer speaker and phone speaker so try them out on both. Good Luck!