Remote for D800
There is the free Helicon Remote Android App for tablets & smartphones you connect the phone to the camera with a OTG USB adaptor & the cameras USB lead.
You can only save jpegs if you want to save raws you have to buy the program costs $48.
I tested it with the D800 & Samsung S3 phone & everything worked.
there is a guy here running this in euro on new sony z phone - says works well...