The best "countermeasure" is...not to get caught.
Now I may sound like a smarta.. and I agree to some point. But this is really the BEST countermeasure to avoid getting a ticket.
How not to get caught? Simple but effective: by using common sense on a public street.
I try to explain: of course nobody really respects 100% the existing speed limits. But a good driver doesn't drive 100 mph in downtown or 50 mph in front of a school.
So how not to get caught? By using your brain, your eyes and your stomach. When driving fast (or even when driving slowly), your brain and eyes should permanently "judge" the current driving conditions and driving situation, including street quality, traffic density, pedestrian density, stop lights, buildings, traffic signs, cars parked on the right, weather conditions, etc.
So how the heck should this help to avoid getting caught? Simple: if you're carefully paying attention to the things happening around you, you'll certainly get to see a photo radar, video patrol car or even a laser gun pointing at you. Now you tell me you can't pay THAT much attention and you can't see THAT much or THAT far? Then...you're too fast. Another simple fact.
In the past 20 years, I never got caught speeding. I always "smell" photo radar, light sensor traps or even laser guns (happened only twice in Italy).
I have a very good eye-sight and 175% "clarity", I can see very far and very clearly. This is a huge advantage, I admit but there is also common sense. If there is a street in the city where only 60 kph are permitted and this street has two lanes for each direction and even goes straight for a few km, there is a very good chance that police will check the speed because it is "easy money" for them.
I could give you more examples but again: COMMON SENSE is a good start. And if you say you saw the photo radar but it was too late to slow down, then you were TOO FAST. Imagine this wasn't a photo radar but a little kid running over the street or a car exiting a parking lot.
When driving, I like it a lot to watch people how they drive and do some sort of analysis because it helps me too to become a better driver. I'd say that around 70% are driving like jerks, not using the turning lights, not maintaining a constant speed, braking too late, not keeping a safe distance to the car in front of them, etc.
A good driver has a good brain-arms-foot coordination.
Meaning: at the same time he can look in the mirror(s), activate the turning light, brake, turn the steering wheel AND watch the things happening around him. How many people do that?
And before I really start to sound like a smarta.. or even worst, like a teacher, a last word from my racing "mentor":
"If you're driving like a jerk on the street, you're very likely driving like a jerk on the track too, meaning you're not a good driver.". He was always very upset regarding those amateur track drivers with a "knife between their teeth". On a public street, the "knife between the teeth" can kill people, it can kill YOU and it certainly isn't a good approach to become a "good" driver.
So if you want a radar/laser warner, get one. But make sure it is an additional help, not a gadget which helps you turn off your brains and shut your eyes. Because there are always video patrol cars out there, there are always light sensor traps out there and in some countries (like Austria or France for example), it is just enough if a policeman says you were too fast without any proof.
Drive safely and use your COMMON SENSE. It works, try it.