Hello, its ObscureClockwork

So i made a door unlock with key return. You input the correct key (this case, redstone) and you will receive it back after it sends an output. If it is incorrect, the bad key is retrievable from the hopper at ground level. Furthermore, it requires only 23 copies of the key (1 for the player, 22 for the hopper)

Please diamond if you like the upload

Pros

• Small, only 1 wide
  
  
• All components underground.
  
• Returns key
  
• Retrievable failures
  
• minimal redstone required
  
  

Cons

• Only returns one key (so if you put a stack of keys, you only get one back)
  
• No output for key failures
  
• Uses 3 hoppers
  
  

Additional Notes

World save contains 3 different versions, one with door, one with chest at ground level, and one with chest at one above ground level

Stair is for retreival