I have a dectector - snooper 815 and it says it has 'stealth technology' so the police can not detect it. But, this is a risk that you may or may not want to take. I won't be.
The fines are rather large for motoring offences and seem quite arbitory. Some one I know was fined for speeding £500 on the spot!(though they WERE speeding!). The Police drove him to a cash point at the supermarket and he had to withdraw the money there and then - £250 from his account and more annoyingly for his wife, £250 from hers! If he didn't pay he wasn't going home as they confiscated their passports!!
The risks are high and probably not worth taking, and £500 will buy alot of Biere!
All the best
Chrissy Boy