Vehicle Electronic Counter Measures

This consists of several parts: 4 antennae that stick out horizontally from the front and rear of your vehicle, on the sides so that your vehicle has a fork-like appearance in the front and back. They would look something like refueling probes on naval aircraft and helicopters. Also, there is a multi-directional pod on the roof, similar in appearance to the DIRCM countermeasure system on modern military aircraft, only smaller, about the size of a billiard ball.

When the front antennae pass through a cop's radar/lidar/laser beam, the antenna itself having too narrow a profile to set off the beam, it detects the presence of the beam, and relays this data to the pod, which rotates to face the source of the beam and sends a countersignal, which sets and holds the speed gun's display to a legal number until the rear antennae pass through the beam, then releases its hold on the source.

The policeman, seeing your vehicle pass, looks at the gun's display, sees a number well within the legal limit, and happily returns his attention to his neglected doughnuts and coffee, peacefully unaware that he has just been duped.

(edit) multiple pods could be installed to dupe several cops at the same time. Particularly useful on Superbowl Sunday, when I got my first ticket ever, having been pulled over more times than I can count without a single ticket during regular days.

(sub-edit) These pods could also be disguised as simple ornaments, mounted on the hood and trunk of a vehicle instead of on the roof.