Door Closer

Somebody always forgets. You sprint out to finish a wounded roamer, your teammate logs off from the kitchen, and the front door stays wide open for the next hour. Fitted to a door, this little arm swings it shut by itself a short while after nobody is using it.

A closed door with a code lock on it is locked again, so together they turn forgetfulness into nothing worse than a slammed door. Put one where people run through in a hurry: the main entrance, the airlock, the door to your loot room. The sheet metal door at the front is usually the first candidate.

Getting one is the catch. Nobody can craft or research a closer, so the metal fragments and the metal spring listed beside it are never spent: it only comes from loot or a trade. Keep your springs for guns, and when a closer does turn up, fit it right away instead of leaving it in a box for a week. It pays for itself the first time it saves your loot.