[Chirael]

Of the "lock box" type key holders, it seems like the Kidde mini-safe box is pretty decent (see https://www.youtube.com/watch?v=ZLg86_C7rrs) - though it's not a doorknob hanger so to install it properly you'd want to screw it into something sturdy.

[somewhereoutth]

seems like they have ones with a shackle: https://www.kidde.com/home-safety/en/us/products/key-securit...