The Room 502 Key is a key that leads to the UFO Ending of Silent Hill: Origins. The game must be finished at least once to obtain this key. After Travis Grady wakes up in front of Alchemilla Hospital, after the events in Alessa Gillespie's house, he can go to the post office and find the key on top of the fire escape.
At the end of the game, Travis goes to the Riverside Motel, where he tries to unlock room 502 with the key. The key doesn't work, and a spaceship carrying an alien and a dog descends. After doing this, Travis acquires the Tesla Rifle.