Man, Yesterday I went to my brother's house and on the way there, I saw a cord going from the seat of the pickup truck to the rear view mirror. Then I saw it, a RD. The passenger then rolled up his tinted window so I would stop looking (I was sorta obvious) but you still could see the cord and the RD.
The RD was right above the Rear View Mirror and it was a great hiding place, I would have never noticed it, but for the cord. I don't know, I just thought that was a really bad idea to do that. That is why mine is hardwired in.