A device that snaps a photograph of a car's license plate (as well as the driver's face, in some states), when sensors installed into the intersection detect that the driver has ran the red light. A ticket is then mailed to the owner of the car, whether or not he was driving it at the time.
IMHO,There are many serious problems with red light cameras that have prompted myriad class action lawsuits, recalls, and court cases. First, the manufacturer of the camera usually receives a quite generous cut of the fine money. Second, if the owner was not driving the car at the time, he still is responsible for the fine. The only way out is to blame it on someone else, and the person blamed has to agree to accept responsibility. Third, many of the cameras are modified to snap pictures without the driver actually running the red light. This is an effort to increase the amount of fines produced.
It is obvious that money drives these cameras. The proponents say that it promotes safety, but several studies confirm that extending the yellow light duration one or two seconds decreases accidents much more than red light cameras do. In fact, there is only one problem with extending the yellow light duration: no money for the city.
I have been "framed" by one of these modified cameras. I was driving when I saw a yellow light. Not wanting to slam the brakes on the wet road, I went through the intersection at normal speed. I got snapped, and the ticket came in the mail. I studied it, and found something queer: the first photograph showed the car's rear axle crossing the line 0.19 seconds after the light turned red. (all the sample photographs showed the car not yet crossing the line) Using my car's speed at the time (44 mph, as printed on the photo), and the car's measurement from the rear axle to the front, I determined that the light had not yet turned red when the car broke the plane of the intersection. I filed for a court date, and told the court my defense. I was still found guilty, on the basis that my defense was not one of the "acceptable red light camera defenses" stated in the applicable statute. ("Acceptable" defenses?! How fascist can you get?). So I got charged the maximum fine allowed by law ($25 more than the original) plus $20 court fee. I can't wait to get that paintball gun for Christmas...