For this, just wire up the hardware (arduino+keypad) as described earlier. Although the code is an entry-level one, it includes a secret key option that will need to be entered on the keypad.

[Andrea] just sent us this great student hack he made for his room. He’s constructed an Arduino keypad door lock — without using any proper fastening hardware! The entire build is made … ...

Not overly confident in his code, he also has it reset every 5 minutes of idling to safeguard against potential memory leaks — probably a good idea!