GPS marked warning zones are handy - I use the proximity warning feature on my GPS to do this for me. As for warning against false signals, I am less confident. The problem is that false signals from some sources are used by police to mask their presence.

Once you get used to being hit with a false signal you don't pay attention anymore and WHAM! There's a speed trap for real. Not so much with X-Band and places where you pretty much know there's not trap - but on the highway for sure. I have developed a habit of double checking before I assume the "usual false alert" is false. More than once I was glad I did...