It's a fact.  Some pests can't stand ultrasonic frequency.  This kit generates an ultrasonic signal that oscillates between 18kHz and 82kHz every couple of seconds.  Has a range of about 10 feet.

Components:  4 resistors, 2 capacitors, LED, 2 transistors, IC, speaker, slide switch, battery snap

Principles taught:  ultrasonics, voltage controlled oscillator, transistors