What happens with laser guns is (even the best ones) will simply not lock on when being jammed.. I'm no expert but I have read LOTS of material on the issue, as well as seen countless videos of jammers being used (mostly agains the Kustom Prolaser III which is one of the best, and most commonly used laser guns available to most Law enforcement.
The unit will not register a speed, and the laser detector accompanying the jammer will go absolutely apeshit.. depending on the mounting of the jammer, reflective surfaces, and believe it or not COLOR of your car, the cop will take some time to get a reading. The display will be pretty much blank for the cop until you get close. In some cases, like if you have a black, curvy car, and/or a really well set up jammer system, you will punch through (ie. not register a speed) right up until you are face to face with the cop lasering you.
The whole idea here is that you slow down to well below the posted speed limit when your laser detector goes off, and even if the cop manages to lock in a reading, you will have slowed down.
I'd say on average the, a good jammer will give you about 5 to 7 seconds maybe? which is plenty of time to slow down. A laser detector without a jammer is useless because by the time it alerts you, the cop has got your speed, and you're about to be pulled over.
I hope this info helps, and if theres anything more I can add, please lemme know.
as far as a ticket for 3mph over? that's the most rediculous thing i've ever heard. fight it in court and simply ask the cop (upon cross-examination) if he was able to visually estimate your speed prior to lasering you. He will probably say "yes, i visually observed the defendant's vehicle traveling at a high rate of speed or ~60mph" or something to the like and all you'll have to do is ask him if he can visually tell the difference between 55 and 56, then ask if he can tell diff between 56 and 57, then 57 and 58. If he says yes to any of the above, tell him he is supercop, because that is impossible. If he is honest, he will say no, and you do not need to ask any further questions to jeopardize your argument. When he leaves the stand, tell the judge that it would have been impossible for him to visually estimate your speed prior to obtaining it from the laser unit, and that you do not feel that this speeding charge was properly justified/laid.
As for speedometer error, it may be true, but i would not use it in court. The first thing the prosecuting attorney will ask is 1) has your speedometer been calibrated (of course, you'll say no, unless you're driving a land speed test vehicle, or a police interceptor), and if he has balls, he might go on to say that 2) you could have a speedo in your car that says you were doing 40, but its still your obligation to drive within the posted speed limit, and bottom line, that laser unit gets tested twice for every session in which its used.
I hope this info helps you, and best of luck!
If you have any questions, I can do my best to help solve them for you!
PS- in ontario, anything less than 15km/h over isn't considered speeding. Meaning, they can't really charge you. I've heard of cases, but its absolutely rediculous. Cops and judges here recognize that you're not posing a threat by driving up to 10km/h (8mph?) over the limit because it would be nearly impossible to limit your speed to EXACTLY the posted speed limit. There are moments (ie, going down a hill, or before you begin to decelerate) that ANY honest citizen will be going a little over the speed limit........ sorry to hear that they are so anile in your state.
