Slightly off tangent, but my local council have been experimenting with 'sonic speakers' in area's of heavily used youth presence. Apparently these speakers give out a 'noise' only noticeable to people of certain age groups. The 'noise' is suppose to be very annoying to the people within the certain age groups, and feedback from surveys seems to suggest this scheme is working.No expensive cctv's required!.
I'm guessing you are just joking Bob. I'm pretty sure that if you were a criminal, unknowingly being captured on CCTV and an announcement was made over the attached speakers, you'd scarper pretty quick - particularly if it said 'the police are on their way'.