Minecraft wiki entry for Secret_door, associated text: This trigger can be completely hidden except for a jukebox. When a player selects and inserts the correct disc, it opens the door. When a comparator is placed next to a jukebox, it can produce a redstone signal which is unique for each disc. This method essentially acts as a key or password, since the player must use the correct disc to access the door. In addition, a jukebox is typically used as decoration rather than a redstone component, leading to a better hidden entrance. The only problem with this, however, is that the door will remain open for the duration of the song (the disc is automatically ejected from the jukebox afterwards) or until another player removes the disc.