The e-Reader is an add-on device for the Game Boy Advance released in 2002 that can read dot codes on special cards and interpret them into data. Depending on the card, the data may contain either information or some type of minigame. Several complete Nintendo Entertainment System games were also made available on special packs of cards. It took a total of nine or ten dot codes (two per card) to store the data of an NES game. Four series of e-Reader cards were released for use with Animal Crossing. Some cards featured Mario-themed designs that could be uploaded into the game. One card even rewarded the player with a copy of Mario Bros. to place in their home.
Additionally, the Nintendo DS, while compatible with Game Boy Advance games, was not designed to work with the e-Reader, but it can be modified to fit in. It works on a Nintendo DS or DS Lite if the player were to open up the e-Reader and remove the Game Boy Advance Link Cable extension wires. The device was never released in Europe, and e-Reader functionality was absent in the European versions of the respective games. The device is compatible with the Game Boy Advance SP; however, it doesn't mount evenly.
In Japan, there were two versions of the e-Reader. The first, called the "Card e-Reader", had no linking capabilities, and thus was unable to be used for games such as Super Mario Advance 4: Super Mario Bros. 3. Later, Nintendo added linking capabilities, releasing this new version as the "Card e-Reader +". By the time the e-Reader was released in North America, the updated version had already been released in Japan, therefore North America never got the original version, instead getting the "Card e-Reader +" under the name "e-Reader".
The e-Reader was packaged with a classic NES game (either Donkey Kong Jr. or Pinball) and a "sampler pack" containing an Animal Crossing card, three Pokémon cards (Machop, Machoke, and Machamp) that allowed a minigame to be played, and a Game & Watch card that contained Manhole. Australian copies also included an Air Hockey game.