This is true in my Pathfinder but I believe its the same with the X. You have constant 12V power in the map lights on the roof. You can splice in there and get juice to your detector. Issue is that its full time power and you'll have to turn the detector off by hand.

You can run power from a switch connection in the fuse box but thats a lot more work. I opted for the simpler design. It also keep the cord from dangling in my view as I drive. It goes UP form the detector, not down towards the dash.