Laser can be very hit and miss, especially at a distance. It could take the cops 3+ shots at reading your speed which is heaps of time for the detector to let ya know what is going on and you can adjust your speed if necessary.

The cops know this and so thats how you can often getaway with a jammer device because the cops receive an error and having to recheck the speed giving you the time to adjust your speed and then turn the jammer off so as you get closer they can check your speed and they are none the wiser that you have a very illegal laser jammer. If you drive past a cop who is trying to speed check you with a laser gun and they cant due to you jammer still being on be prepared to be pulled over and charged with obstructing police.