I used to have an actual police siren in my mustang. They can be bought for next to nothing at city auctions. I just bolted it under my car beside one of the wheel wells. Worked like a champ. In my truck, I went to a junkyard and bought 5 different electric horns for $2 a piece, and hooked 'em all up in parallel. When I hit that horn, I had 5 different tones all shrieking at once. Sounded like a friggin train!

Ahh... I miss my old police siren. I lost it when I hit a pothole and the speaker caught the lip of the pothole. The whole thing just went bouncing down the road. Oh well.

In college, all my friends and I had CB's with PA's attached. We'd set my CB to use the loudspeaker, tune to an odd channel, park in the mall parking lot, drive in his car across the parking lot and mess with people coming out of the building. Also fun is using a scanner to intercept the McDonalds Drive-In feed and broadcast THAT over the PA. People get real upset when they hear themselves coming from a loudspeaker somewhere. Ahh.... the good ol' days.