A laser detector is normally "you just got popped". It might detect sporadic reflections now and again. It might detect the laser at a longer range than the laser gun is able to (or legally allowed to ...) get a speed reading.
Instant-on radar doesn't do you a whole lot of good to detect, either, unless it can detect the radar being used on other vehicles in your vicinity. If there are other vehicles in your vicinity, it's probably better to just not be the vehicle that's attracting attention.
Thinking to yourself, "If I were a cop and my day's assignment is to write speeding tickets, where would I want to set up?" is a good thing to do.
Likewise, "This speed limit is abnormally low, and would be a prime spot to write tickets. Hmmm."