The only thing I can recall is my mother got one way back in the mid to late 90s. I used it one time and any time you would pass a grocery store or any other place that had automatic opening doors, it would go crazy. Chances are the police have a radar to detect those as well and if you ever are pulled over, they will be more likely to give you a ticket. I've heard that in some states they will take them from you and ticket you if they catch you with one. Another factor is, I think considering what they do for a living, they have a pretty good idea of how to beat the system by being able to block the system from catching on to them until it's too late.