Instructions
Emulator Cheating
Download and install an emulator such as Visual Boy Advance or No$gba.
Load your "Pokemon Ruby" ROM file and start a new game or load a save.
Add a new cheat to the cheats list. In Visual Boy Advance, select the "Cheats" menu, choose "Cheat List" and click "Add New Cheat." In No$gba, click "Options," choose "Cheats" and lastly "Add New."
Enter the following code into the dialog box: "E03B0649 5D67050C 78DA95DF 44018CB4." This code will enable the Walk Through Walls cheat, allowing you to walk nearly anywhere.
Game Boy Advance with Action Replay
Insert your Action Replay into your Game Boy Advance and insert your "Pokemon Ruby" cartridge into the game slot on the device.
Enter the code "DE00AAFD 2EBD05D0 530823D9 16558191" when prompted. This is the master code for "Pokemon Ruby." This code must be entered to enable any further codes when using the Action Replay device.
Use the code "E03B0649 5D67050C 78DA95DF 44018CB4" to enable the Walk Through Walls cheat.