I have an issue with this though – since the sound is inaudible to humans, how would one notice if the device is maybe jammed and producing the ultrasonic tone non-stop? Even if it isn’t harmful it will still have an impact on the animals psyche over time I believe. But I guess that’s what the LED is there for – it will probably light up when it’s active.
It might still misfire though – not sure if it can really distinguish all kinds of dog barks so perfectly without misfiring on other sounds that are similar or eventually coming from the TV or other media.