Why do people complain about Mosquito devices? Even if you can hear them, you only hear them when you're very near to them. They don't do any harm to anyone, they're merely unpleasant to listen to. They're usually fixed on the outside of shops. Simply don't hang around pointlessly outside shops and they won't affect you. Why do groups of nuisance youths hang around anyway? What do they say to each other beforehand? Something like: "I've got a great idea for what to do this evening - let's hang around in front of the local shops for a couple of hours, shouting and being a pain in the arse to everyone around us!" Then his friends say: "Yes - you're the king of good ideas - that's a great plan!",(reply>), "Very near" depends on your hearing. Mine has recently worsened a lot, but a few years ago I could hear it from 20 meters away, keeping me out of a bit of public park whenever the school nearby was closed and they turned that on to keep teens away from school grounds.