Hidden wall outlet safe:

Print the Outlet_Safe.stl file. Using a real receptacle, remove the mounting screws from the yoke (metal ends). Use a real receptacle outlet plate and screw the plate to the receptacle using a plate screw. (I used real receptacle and outlet cover so it matches the house exactly) Use two rubber band and attach them as shown in the photo by looping them around the two rubber band mounting holes. Loop the ends of the rubber band between the real receptacle plate and the metal yoke to hold the receptacle and plate to the wall box as seen in the picture.

If your plate is too loose, use smaller rubber bands or rotate the outlet and plate a few times knotting up the rubber band and it will fit snug.

I made two holes in the box to screw the box onto a wall stud.

I made this very simple but it is very effective and kinda cool too!