From NintendoWiki, your source on Nintendo Information. By Fans, For Fans.
The Nintendo 3DS NFC Reader/Writer is an accessory for the Nintendo 3DS, Nintendo 3DS XL, and Nintendo 2DS that allows for compatibility with near-field communication-based technology, namely amiibo. The peripheral was released in 2015, alongside Animal Crossing: Happy Home Designer, which it was also released as part of a bundle with. It is incompatible with the New Nintendo 3DS and New Nintendo 3DS XL systems, since the two already have built-in NFC sensors on their touch screens. The NFC Reader/Writer is powered with two AA batteries, and uses an infrared signal to connect to the console.
Using the Nintendo 3DS NFC Reader/Writer