I set my original Amazon Echo on a small shelf against the wall, and created this retaining ring to keep it from falling over if someone bumps into it. The ring mounts to the wall.

I've included a bonus stencil which can be used to perfectly locate drilling holes.

You can screw the ring into the wall from the front, or optionally put nuts in the pockets and bolt it from behind (through the rear panel of the shelf, as I did).