Long ago, I heard of someone who had a hand-held radar gun, similar to what the police use, who liked to aim it at speeding drivers and watch their brake lights come on.
I know someone else who would have fun with this. His birthday is coming up. Where could you get something like this, that would trigger radar detectors in cars?
Signed, Low and Childish Sense of Humor
Here you go. Knock yourself out. Just don’t get caught by anybody, including the people you’re screwing with.
I think I saw one at Radio Shack.
Hell dude if it is just for fun use a hair dryer. 
The name of the game is Trolling for Taillights
EBAY
is a great place to get an actual police unit. Search for “radar gun” or “police radar”.
Just make sure to get a K-band or Ka band unit, as the Fuzzbuster crowd tends to ignor X-band warnings because very few police agencies use X-band anymore, and most false alarms are on X-band.
To the best of my knowledge you no longer need an FCC license to possess/operate a radar gun. But check local laws before partaking in the fun-n-games.
Damn. You beat me to it!
Thanks, guys, just what was needed! off to get into mischief