I think it's the radar detectors that are outlawed, my understanding is you don't even have to have it on, it's illegal to own one over there. I don't risk it with mine, I leave it safely at home!!
I guess the GPS ones are ok though??
That may be the way things will go in the UK as well this time next year if the government get their way

So I'll have a worthless and illegal detector in my car

There was a short piece on 5th Gear on Channel 5 about it.