Keycards are items which allow the player to access different parts of the facility. All keycards have a distinct color and can be identified from a distance.
Keycards are essential if a player wants to go anywhere in the facility, as checkpoints, gates, containment chambers, and certain doors and lockers require them to enter.
There are currently 12 keycards ingame.
When hovering over a keycard in the inventory, a small group of squares are shown. These represent what the keycard can or cannot unlock, known as its access tier. Normally lit squares mean the keycard has the access tier, while dark squares mean that it doesn't.
Keycards must be equipped to be used. To equip a keycard, open the inventory by pressing Tab ↹, then select the keycard with Left Click. Then approach a door that requires a keycard and press E.
It should be noted that while the O5 Keycard is the best keycard in the game, it is not the best idea to go for it as it takes some time to get it. It is often best to stop at Facility Manager Keycard or a Commander Keycard as both of these can open most doors, with the Facility Manager being able to open the Nuke and 106's CC.