When the German police halts you (for some reason e.g. after an accident or a traffic violation or suspected intoxication) they can check your GPS. When they find evidence of speedcams (in Germany!!) then can punish you. However a few years ago a judge did conclude the specific legislation was not watertight and not legitable and the offenders get off free of any punishment. I haven't heard of a newer corrected law since, nor can I garantee that you won't get fined at all when the police finds speedcam files. I heard the police checks no more since.
That is in Germany and Germany only!!!!
In Switzerland and Austria you will get fined and the device will get confiscated! How they do that with an inbuild device is unclear to me.
In France, I know it's forbidden as well, though your GPS may give warnings for and show "danger zones" which of course are speedscams :D