You check the doors...

Wandering up and down the hallway, you count that there are eleven rooms in total. Your room was number four, so you decided to head next door to number five. Pushing down the handle, you find that it's unlocked.

"Ah. Okay. I'll check each rooms before I actually go in." You mutter to yourself as you walk up and down the hallway checking each door except your own.

After a few moments of checking, you find that the doors 1, 3, 5, 7 and 11 are all locked, meanwhile the other doors are all unlocked, with the last one on your room's side having a fairly peculiar odour coming from it.