Real cartridges use a special translucent black plastic that glows red when held up to a bright light (due to the IR sensor for the Pokéwalker).

Typing hex codes is tedious. The "QR codes" you see online are often these codes converted into a scannable image for PC emulators only . Do not scan them with a cell phone; they will just show a string of numbers.

While Pokémon HeartGold was originally released for the Nintendo DS and did include a built-in QR code feature, modern players utilize QR codes for homebrew installation, save management, and cross-generation transfers. How QR Codes are Used with HeartGold Today

A specific permanent QR code exists that allows you to claim the Mythical Magearna once you’ve beaten the Alola Elite Four. Safety and Legitimacy Tips