Laser speed guns transmit short bursts of infrared light that bounce off a target vehicle and return to the laser gun. By timing the outgoing and return trips of the light bursts, it can compute the target's speed. The laser's biggest selling point is its narrow beam—no more than three feet wide at 1,000 feet—a feature that provides nearly foolproof target identification.
In comparison, a radar beam is about 100 to 200 feet wide at the same distance. Using this veritable blunderbuss demands more involvement by the officer, particularly when it's used in moving mode. Learn more about police radar.
Their target-specific capability is why lasers are the tool of choice in town, especially on multi-lane, heavily-traveled roadways. In the presence of multiple targets, radar is frequently helpless, merely displaying the speed of the strongest or, on some models, both the strongest and fastest targets. But it's up to the officer to determine which vehicles are producing these speeds. In dense traffic that's often impossible.
A laser can easily shoot into a clump of traffic and single out a high-roller. Faced by radar, this same vehicle would likely be protected by others nearby. But confronted by a laser, it's nigh impossible to hide among slower vehicles.
Laser guns must be used from a stationary position and are most effective at short range, usually targeting traffic at 800 feet or less in town, about twice that in open country. We've tested lasers that clocked pickups and SUVs at 6,500 feet but in the real world, that kind of range is useless. Just like with radar, the officer is still required to identify his target.
Laser detection is much tougher than radar detection. Since the narrow laser beam generates very little scatter—random bits of electromagnetic energy bouncing down the road—it is much tougher to detect than a radar gun that blankets the countryside with its powerful, easily detectable microwave beam.
Laser guns operate in instant-on mode, not transmitting until the trigger is squeezed. For this reason don't expect a warning from a detector. Similar to instant-on radar, if you're the target there will be zero time to slow down. Your only hope is to use a good laser jammer.
Laser jammers are legal in most states and the good ones are more than a match for a laser gun.