Internet Pecute Ultrasonic (above 20 kHz) Pet Dog Repeller is type I have. Video below shows how well it doesn't work. At least, I know I am not alone.
https://www.youtube.com/watch?v=pu7mHw6YnoE
Left circuit is 9 volt battery supply and power on LED that lights when pushbutton switch is pressed. It goes through circuit board and right circuit is what an oscilloscope shown connected across piezo buzzer terminals. Oscilloscope showed much sharper spikes. Since piezo buzzer seems not to work l left 20 K ohm out of circuit.
Looks like I need a real piezoelectric buzzer if I get hound hearing sound output.
