Ok, dont ask me about the physics on this one - i'm sure someone will have something to say on the matter..
but, here goes..
How about using a very precise directional speaker that can be aimed at the window of another vehicle and the sound waves are modified in a way that they are specifically designed to resonate off the glass - therefore creating a direct audio link from a police vehicle and the offender, without creating a massive distorted noise that is associated with a traditional megaphone.
It would be good for negotiations (ok, only one way) with fleeing felons, or even as an efficient way of warning minor offenders without having to pull them over.
Of course, put into civillian hands - would be great for road rage ...-- bod, Apr 05 2004 FULLY BAKED http://www.usatoday...003-05-19-hss_x.htm: Ultrasonic speaker [MySoulWanders, Oct 04 2004] FULLY BAKED http://www.amazing1.com/laser2.htmLaser Audio Pickup [MySoulWanders, Oct 04 2004] perhaps I *should* charge for this service. http://www.ingenius.bc.ca/ [po, Oct 04 2004] Voice of God on the Road http://www.halfbake...D_20on_20the_20roadAlternate solution was halfbaked by [James Newton] [krelnik, Oct 04 2004] I think this is a pretty good idea, I'd rather have one myself, cops already got plenty of intimidating equipment.-- dentworth, Apr 05 2004 Highly directional speakers are with us today - the army is using them in Iraq at road blocks, advertisers are thinking about using them to target individual shoppers like something out of Minority Report.-- DrCurry, Apr 05 2004 I belive if you look on the POPULAR SCIENCE website and the TECHTV website, they have listed a a ultrasonic speaker that does what you describe. It uses tuned ultrasonics to shoot a coherent beam of inaudible sound , that becomes audiable again once it hits a solid surface ( such as glass ). I think the system runs for around $300 -$400.
It can become 'Two-Way' with the use of a modified LASER audio pickup. A version of this is also available for sale ($350-$500) on the other link.-- MySoulWanders, Apr 05 2004 ok.. so its been done. For once i havent had a completely unfeasable idea!!-- bod, Apr 05 2004 who is Ingenuis?-- po, Apr 06 2004 One of those dot com companies, I think.-- DrCurry, Apr 06 2004 thought it was a cat litter firm, silly me.-- po, Apr 06 2004 random, halfbakery