Nintendo E-Reader
The e-Reader (カードeリーダー, Kādo Ī Rīdā?, Card e-Reader) is a device made by Nintendo for its Game Boy Advance portable video game system. It was first released in Japan in December 2001, with a North American release following in September 2002. It has a 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. See below for a comprehensive list of cards and their functions. The cards themselves contain data, as opposed to unlocking data already on the device itself.
The e-Reader is neither a console nor an accessory, but an add-on device, like the Famicom Disk System or the Sega CD. The e-Reader is one of only three official Nintendo add-ons to be released in North America. The other two are the Super Nintendo Entertainment System's Super Game Boy and the Nintendo GameCube's Game Boy Player.
Read more about Nintendo E-Reader: General Information, Compatibility