Ed Paradis of the Dallas Personal Robotics Group did a write up about hacking the Hot Wheels Radar Gun. The toy radar gun works very much like a real one, using a 10.525 GHz signal to clock the speed of cars or whatever you want to point it at. Because of the low price ($30 or less) and a recent mention in Make's blog there's been a lot of interest among hardware hackers. By adding a some new circuitry on a breadboard, Ed was able to do some experimentation to determine if the Radar Gun could be adapted for use on mobile robots. His page includes detailed descriptions, plenty of close up photos of the disassembly, and pointers on integrating the radar gun parts into your own circuits.