This is a very interesting concept that could solve a common problem for cat owners. It’s the KnobLock, a simple little device designed to keep cats from opening lever-style door knobs. The foam piece slides over the lever, preventing the cat from pulling on it and opening the door. It looks like it can also be used to prop a door open by attaching it to the edge of the door. I haven’t tried one myself, so I’m not sure how well it works, but cat-proofing lever door knobs is something that I’ve had readers ask about and this could do the trick.