Where would you find the braille decoder in fire red?

In Pokémon FireRed, you can find the Braille decoder in the Pokémon Center in Saffron City. After obtaining the Ruby and Sapphire from Team Rocket's hideout, you can return to the center and talk to the woman in the back room. She will give you the Braille decoder, which helps you interpret Braille messages found in the game, particularly in the cave areas.