Nintendo e-Reader Cards

The Nintendo e-Reader,[a] commonly abbreviated as e-Reader, is an add-on manufactured by Nintendo for its Game Boy Advance handheld video game console. It has an LED scanner that reads "e-Reader cards", paper cards with specially encoded data printed on them.

Depending on the card and associated game, the e-cards are typically used in a key-like function to unlock secret items, levels, or play mini-games when swiped through the reader. The cards themselves contain data, as opposed to unlocking data already on the device itself!