The Key to Room 4 (Japanese: 4ごうしつのカギ Room No. 4 Key), known as the Rm. 4 Key in Generation III, is a Key Item introduced in Generation III.
The Key to Room 4 unlocks the door to Room 4 inside the Abandoned ShipRSE/Sea MauvilleORAS, and is part of the puzzle to obtain the ScannerRSE/Storage KeyORAS. It breaks upon using it, consuming the item.