Rodents and insects (including mosquitoes) are allergic to high frequencies above 15kHz. My repeller is using this fact. This repeller generates ultrasonic tone that is inaudible to humans and harmless, but reliably repels uninvited guests such as mosquitoes, mice, rats, marten or spiders. This version is improved by the periodic change of frequency, so the insect and animals can not build the immunity against the ultrasonic tone. Switching frequency is realized by changing the voltage at 5th pin of circuit 555. These voltage changes are ensured by the blinking LED. The frequency changes range between about 24 - 29kHz. The source of ultrasound is piezoelectric speaker (beeper).