K9F wrote:

My kids can hear the ones I have in the garden. The older generation such as myself hear diddly squitt! I believe certain villages have had them fitted in certain locations to prevent youths congregating and being unsociable in key areas too.

**Edit** You can actually buy the anti loitering devices on the net. Handy if you find youths chewing your tyres or leaving teeth marks in your soft A Bar perhaps too.

http://www.compoundsecurity.co.uk/security...ing-device