Illegal.
Based on this:
It is a felony to impede the lawful action of any law enforcement officer.
By using a radar detector, you are attempting to avoid or fraud a legal effort on their behalf to catch speeders.
The device itself is legal. To use it, is entirely not.
You do know that you have an anti-ticket device in your car already, right? It's called your foot. Take it off the gas pedal, and go the speed limit. No tickets, no getting pulled over. Amazing.
