I actually have my radar detector installed in my car above the sun visor with the wiring hidden behind the pillar cover, then under the dash, hard wired into my console cigarette lighter. You can't see the detector or the wiring, works great.
This is what I found about legality:
Radar laser detectors are legal to own and operate in passenger vehicles in the state of Oklahoma.
Currently the only state that it is illegal to operate a radar detector is Virginia and Washington D.C.
Laser jammers are illegal to operate in the states of: Nebraska, Minnesota, Utah, California, Oklahoma, Virginia, Colorado and Washington DC.
Radar jammers are illegal to own and/or operate in all 50 states per the Federal Communications Commission.
Radar detectors are also illegal in commercial vehicles weighing over 10,000 pounds in all fifty states, per Title 49 Transportation Act.
Radar detectors are also illegal to operate on any military base.
So, it's not illegal where I live, but it does make them angry if they hear it going off, lol