Cheating devices, also known as Game-altering devices are devices that are often used for cheating in video games, and various commercial cheating devices are advertised for this purpose. As well as cheating, cheating devices can be as a means to access unused content, hinder the player, or corrupt the memory/save file, if codes are used indiscriminately.
One of the ways a cheating devices may be used is by inserting a game cartridge into another cartridge; called a cheat cartridge and then inserting the cheat cartridge into the system to activate codes once the system is powered on. This is used by cheating devices such as the Action Replay, GameShark and Xploder. If a system has multiple slots, such as the Nintendo DS models before Nintendo DSi, the cheating device may be inserted into one slot to control gameplay in the other. This system is used by Pro Action Replay for Game Boy Advance. Another way a cheating device may be used is by inserting the cheating device into the system, activating the codes and then ejecting the cheating device and inserting the target game to apply the codes, as is used with the Action Replay DS and its successors.
Cheating devices such as the Action Replay and GameShark traditionally work by writing to a memory address in game constantly, or when a button or button combination is pressed for example, locking the address 0x03000F7A in Densetsu no Starfy to five will cause Starfy to constantly have five hearts regardless if he gets hit or not.
Cheating devices such as the Game Genie work differently by temporarily patching the program code, as in the ROM, meaning it may be possible to cause an effect not possible by modifying the memory.
Another type of cheating device is a device that stores and loads save files into the game, for example, Action Replay Powersaves 3DS, allows players to modify existing save files to apply codes to it. The Mega Memory Card by InterAct works by backing up save files and restoring them, and this can be used in games like the Game Boy Pokémon games to cheat by cloning Pokémon, if a Pokémon is traded to another game and the old save is restored.
Though some cheating devices are sold commercially, cheating devices for Nintendo consoles are neither licensed or endorsed by Nintendo, even though they are generally legal. Cheating devices may come with codes for certain games pre-installed, but the player may be able to enter their own codes found online or through hacking.