Even the most advanced door locks can be cracked, whether they involve a physical key, a key card, or some electronic doo-hickey. But how can you expect to open the door if there’s no knob for you to turn. That’s the thinking behind the “Doorknob Condition” solution, a retractable doorknob that you can pull in from inside the room, preventing anyone from outside of the room from even attempting to open the door.

Designer Arnaud Lapierre created the “Doorknob Condition”, which features a pulley system to retract the entire doorknob. It’s such a simple, yet ingenious solution, proving to be much more effective than that dinky “Do Not Disturb” sign that hotels provide.

Of course, if someone really wanted to come barging in you while you’re doing whatever it is you’re doing, they could just kick the door down, but that’s a different matter altogether.