Capture speed and violations of Traffic Police

Hi there, i'm using Lumix camera with fat gecko camera mount to capture police violations on the roads. But i need something to capture speed also. What kind of device i can use to capture speed and put it together? Youtube Example is attached

http://www.youtube.com/watch?v=6e3STSZuD7w


Regards

You need a speed measuring device obviously while you are taking a video using either a radar or lidar unit. If you really need a better one, it could be pricey like this one in the video link. ‪New 2009 Stalker DSR2X. In Car Video‬‏ - YouTube