Kloofvreter
Honorary Master
If a device warns a motorist of a speed trap and he slows down, or a motorist flashes and warns another one and causes them to slow down, the traffic department should be happy. 
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Do people still pay speeding fines?
But you can report these in Waze so that others at least don't get caught.
Except the Waze one's go through a community review. I've reported the deployable one on the M1 North that usually sits behind the 5.4N sign multiple times, but it has never appeared on the map.