I designed this to hold a keychain remote garage door opener like this https://www.chamberlain.com/keychain-garage-door-remote/p/G956EV-P2MC. We keep a remote in the junk drawer of our kitchen to open our detached garage door from the house. I previously just stuck it to the drawer with 2 sided tape, and was like that for 9 years. I recently needed to take it out of the drawer, and had an idea to design this holder. and it's working great!

The internal dimensions of the holder are 63.5mm tall, 34 mm wide, and 13 mm thick. The cutout comes down about half way to expose the buttons on the remote. Attach with 1 or 2 command strips/foam 2 sided tape. I printed the holder upright, but used a brim to ensure bed adhesion and eliminate the need for supports.

 The remote fits very snugly in the pocket, and that's how I wanted. If you want it to be a bit less snug, or resize to fit your spare remote, increase/decrease the size as needed.