The Binding of Isaac: Antibirth Wiki

Red Key is an unlockable active item.


  • While held, a red outline of a door will appear on walls which a Red Key can be used on.


  • You cannot use the item unless you are close to an outline.
  • In rooms with multiple outlines, it only opens the closest one.
  • A red room can be created through another red room.
  • The red rooms have a physical presence on the floor unlike Devil Rooms or I AM ERROR rooms, and can be re-entered at any time.
  • Red rooms follow secret room rules, meaning that all other rooms it connects to must have clear space for a door to the red room.
    • As a result, all red rooms are symmetrical, and if there's enough empty space you create a large area of red rooms.
  • Although a red room can be adjacent to more than one room, if the room type is one that requires something like a key, each entrance to the room will have its own lock.
  • You cannot build a red room outside the boundary of the map. Trying to do so will open a door which leads to the I AM ERROR room instead, which you cannot return from.
    • You can tell if a red door will lead to an I AM ERROR room if it does not show up on the map.
    • The max boundary size of a map is 13x13 rooms.
  • The max number of rooms in a single floor is 128, counting all the rooms of the original map (including Secret Room and Super Secret Room, also double and quadruple-sized rooms count as one) plus the rooms created. After the count of 128 rooms the Red Key will not open new doors and the charge is wasted.
  • Red rooms can be special rooms even in The Womb / Utero / Corpse, Sheol, Cathedral, Dark Room and The Chest, where these types of rooms otherwise would not be generated.



Bug Bug! After quitting and re-entering the game, using Red Key will cause a no-room-config error until the next floor is reached.
Bug Bug! Using Red Key out of certain special rooms will crash the game.
Bug Bug! Created rooms may interfere with the operation of the room-teleporters in Mausoleum, causing the teleporter to lead to the wrong room.
Bug Bug! Creating a room where the entrance to Mega Satan is makes Mega Satan inaccessible.