I'm not far off 40, and I can hear these. My children are very troubled by them.
There's one close to my home in London W2 which has been sounding continuously for nearly two years.
It's at the bottom of a not particularly dangerous residential block of flats. It hasn't been vandalised, which I hope means that its "target audience" are not all that bothered about it, but I do feel sorry for any small children living nearby. I tried to report it to the Westminster noise complaints line a year or so ago, but with no useful response. Maybe they couldn't hear it. In fact if it wasn't for my children's response, and the fact that the device is visible and looks like the pictures online, I'd probably wonder myself whether I wasn't just imagining it since it doesn't seem to make any difference to other passers-by.
There seems something quite original and wrong about trying to harm other people with a method that you cannot even detect yourself.