Radar detectors detect speed laser guns the same way they detect instant on K and Ka radar. Radar detector alerts are delayed because the digital signal processor (DSP) needs additional time to filter out unwanted incoming signals. So if the radar detector alerts to laser then it is too late since a speed reading only takes .3 of a second from a speed laser gun. 

Speed laser guns were developed to defeat radar detectors and give the police the ability to single out vehicles in traffic. Originally speed laser guns were shot at the windshields of vehicles and there was laser detection on radar detectors. This at least allowed the laser radar detector to sound, even though the speed was already obtained. This also created a glow that gave trailing vehicles with radar detectors a chance at alerting to the laser beam. Police have now been trained to avoid hitting windshields when targeting vehicles to prevent radar detectors from alerting. 

Radar detectors have great difficulty detecting the laser beam because speed laser guns are now aimed at the front of vehicles, away from radar detectors, and not at the windshields where radar detectors could be mounted. Since the laser beam narrows the closer you get to it, the chance of radar detectors alerting becomes lesser the closer the vehicle gets to the speed laser gun. At 1000 feet the laser beam is only 36 inches wide and at 500 feet it narrows to 24 inches wide. That does not allow for an early radar detector warning when a speed laser gun is hitting each vehicle separately with laser. Since the laser beam is not spread over the roadway like radar, the radar detectors can not detect it unless it is pointed directly at the laser radar detector. 

Speed laser guns are normally shot at distances of 500 - 2,000 feet. Radar detectors might alert to farther distances but that does not prevent a ticket. A laser operator usually operates the laser gun at far distances combined with concealment including night use. Most speed traps are setup to prevent early warning so if a laser radar detector alerts you then you have been caught off guard without a chance to check your speed.

The radar detectors available without complete laser coverage: escort radar detectors, valentine radar detectors, whistler radar detectors, bel radar detectors, and cobra radar detectors. Using a radar detector without a Blinder laser jammer is risky because radar detectors do not give early warnings to laser alerts. If the laser radar detector on the radar detector alerts to laser, then there is a good chance that your speed has already been seen. If you use both a Blinder laser jammer and a radar detector, then you are fully protected from both radar and laser threats. Even if the radar detector doesn't catch the incoming laser, the Blinder laser jammer will alert you and jam the laser to give you enough time to check your speed. 

Even the best radar detectors on the market are defeated everyday by speed laser guns. All radar detectors will not provide full protection when up against speed laser guns. Using radar detectors, without a Blinder laser jammer, only gives you a false sense of security without being fully protected from speed laser guns. No radar detector is complete without a Blinder laser jammer.