Ultrasonic cat repellers are often very audible to children I can still hear them slightly at age 20, coupled with my tinittus they cause discomfort and are increddibly annoying. Just worth bearing in mind if you or your neighbours have kids...
and indeed, sound engineers....... and many musicians....
I find them painfully irritating.... and i'm a particularly unpleasant S.O.a.B. when irritated in that manner.... as my neighbours at our old house discovered......
i think suggesting i ram knitting needles in thru their ears to demonstrate what i was feeling when they switched the damn things on might have soured the relationship a little.
pepper dust, citrus peel, and an eagle eye with a water pistol trains them over the course of a couple of weeks,, then change the citrus peel once a month and you're sorted.