Make sure to specify which Resident Evil game you're playing. Each game has its own storyline and set of puzzles.

RE3 Remake introduced more complex, randomized keypad puzzles inside the downtown area. The here refers to the substation puzzle.

Head to the hidden attic area in the house.

Mr. X (The Tyrant) changes your priorities. The exclusive codes you want before he arrives are:

An "exclusive" code refers to a combination that isn't written on a sticky note or a whiteboard. These are the codes hidden in film negatives, dial puzzles, or the infamous "Portable Safe" mechanics.

If you are actually looking for codes in the Resident Evil series often associated with "Resident X" searches: Resident Evil 7