In snapshot 14w04a, Item Frames now give off redstone signal when used with comparators. This can be used to make a locking door requiring combination lock.

Here is how to use 2 Item Frames to making a locking door, requiring players to choose the right item frame number, by spinning the pointer, to unlock the door

Combo Lock Number / Items in Furnace
"1" - 0 items
"2" - 1 item
"3" - 14 items
"4" - 28 items
"5" - 42
"6" - 55
"7" - 1 stack + 5 items
"8" - 1 stack + 19 items

To Download:
Extract the folder "Item Frame Door Lock" into the Minecraft Saves folder (%appdata%.minecraftsaves)

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