A
Gizmodo post about teens using ultrasonic ringtones on their cell phones led me to a link for a page where you can listen to the tones. The 12 tones range from 8kHz to 22.4kHz.
My hearing topped out at a lowly 14.1kHz. If you'd like to try it, be sure not to have your computer speaker volume too high because the sounds are piercing (and much better than cell phone speakers). Oh, and I don't have any critters but if you do, you may want them out of the room when you try this.
Ultrasonic Ringtones