We found this great project while scrolling through some Popular Mechanics.
Corey from Sawdust to Stitches wanted a secure place to keep firearms, and still keep them away from her children. By pulling out one side of the frame, a couple pins are removed that allow the mirror to swing away and reveal her storage behind. Adjustable pegboard allow her to configure the layout however she wants.
She put together a great video showing the features of your creation.
We like how it blends in with the decor and is large enough for plenty of storage, but appears slim and unobtrusive.