Infact, I remember seeing either Car and Driver or Road and Track perform a test on radar jammers. Active jammers (Illegal) were effective within certain distances--limited by the power of your transmitter. Close enough for the transmitter to reach the gun, yet far enough that the gun doesn't "burn thru" the jamming. Basically, even the active jammers were tracked at vary long and short ranges, but worked somewhere in the middle. Passive jammers such as the Rocky Mountain products were worthless. In one test they seemed to increase the distance in which the radar locked on (so I guess they do reflect something). The Lidar (Laser) jammers on the other hand proved to be very effective. However they were still not all that excited about those because driving with your high beams on will also jam laser.