Some police have radar detector detectors. I know, because I was pulled over by the RCMP in Ontario, who claimed i triggered their RDD.
They're apparently not all that reliable, because I didn't have a radar detector. According to the Mounty, it was likely having RDS scanning for traffic reports on my radio that gave a false positive.
The only time I ever was caught speeding, I lost my license for 18 months and got a $2k fine. Not fun.