Maybe a jamming device? Ya gotta be able to hide it on those roadside checks though - you know, for the children.
Spark Gap generator. Shot Noise. Good for about a 10' radius when powered with modest current. We used to make them in high school and get all excited when we pulled up next to a car at a traffic light and their radio would go all static. Very useful when trying to stomp out mom and dad's joy of listening to Debbie Reynolds and Roy Orbison on the oldies station when we worshiped "Freebird". Oddly enough, I love Roy Orbison and Debbie Reynolds today and I'd put my foot up my kid's a$$ for medling with my airwaves.