Most adults can not hear sounds above ~15kHz. This app produces sounds from about 10kHz up to nearly 20kHz! This makes a perfect prank, since it is very hard to determine where the sound is coming from and can even annoy people rooms away!
It is said that ultrasonic frequencies and audio within this range can repel mosquitoes, rodents, teenagers, or other unwanted pests! You can even use it as a dog whistle to train your pets! Choose from 6 different frequencies!
*Note that device volume and speaker hardware capabilities vary among devices so listed frequencies kHz are only roughly accurate.