A:Answer I purchased this for a D7200, not a D800, but it worked after I found the menu option to enable the remote. It was under the "Photo Shooting Menu". Once you enable that the remote worked quite well. This remote appears to be the equivalent of the Nikon ML-L3 Wireless Remote Control, which according to the Nikon website doesn't support the D800.
So it's possible this remote doesn't support your camera.