A laser detector will only warn you after the laser gun has been fired at you and the beam returned to the gun and your speed measured.
A laser jammer consists of the transponder (also a laser) mounted in the grill and the control and warning box inside the cabin. Once a laser gun is fired at you, your transponder intercepts the beam and fires its own beam at a different frequency. It does this for a period of 5 seconds with the alarm sounding. His camera/laser will display an "error" (normally error 7) During these 5 seconds of jamming you have ample time to slow down.
I have been using a Lidatek LE10 brute force jammer for 12 years and never had any problems. In any case I have seen the "speed teams" hiding so far in their nests that it will take a day to get out. I have seen them inside a wheely bin with a hole cut in, Lying next to the N1 inside a "Karoo bossie" with more "Karoo bossies"on his head,1mx1m Shade cloth hides.
They must of course prove that you have been using the device to defeat the ends of justice and to my knowledge it was tried but normally is withdrawn or people pay an admission of guilt fine.
Unfortunately speed trapping has become the no 1 money making business in SA and by that I do not condone speeding but sometimes you get deep in thought on a quiet road and you get caught doing 75 in a 60 zone.
If only so much effort was spend on road safety and patrolling less people would have died but it is not as easy as sitting and hiding in the bushes.