Things You'll Need
Instructions
Insert your "Pokemon Ruby" cartridge into one of the Game Boy Advance systems. Place the E-Reader in the other system.
Connect your two Game Boy Advance systems with a link cable, and power on both of them.
Swipe the special edition "Pokemon Ruby" E-Reader card, which comes packaged with the game, through the E-Reader device. This unlocks the door.
Ride your bicycle or fly to Mossdeep City on the Game Boy Advance system running "Pokemon Ruby."
Walk to the old man's house and approach the door. Press "A" to walk through the door, which will now be unlocked.