Defendius door chain is a maze


Contrary to its Potter-esque spell like command, the Defendius door chain is actually your armor against unwanted break-ins. A product of the Art Lebedev studios, the lock features a maze with enough chain length for you to open the door from inside; but if someone tried to yank the chain from outside won’t be able to do so thanks to the maze-design.


door_chain_2.jpg
Source