An Action Replay is a device for video game consoles that enables gamers to activate hidden secrets and cheats in games. At their most basic level, Action Replay devices require cheat codes, but newer versions are even capable of downloading all the latest cheats directly to your game console.

You can purchase an Action Replay device for your console by following the links below:

GBA SP For all different types of games
GBA SP Just made for pokemon cheats
PS2
DS
Wii

How to add some cheats to your action replay device

Ok. first, update your firmware by using the program provided. then, at the bottom of the AR menu, there is a small * button. click it, and you can add your own codes manually. (or, on the program, drag and drom to the action replay)

More Detail
Action Replay that were capable of saving the system's state to tape or disk operated in broadly the same way. By attaching to the computer's memory bus (via the Zorro expansion slot on the Amiga) all memory access by the processor could be monitored. By keeping track of all writes to hardware registers (for example, to the video or sound hardware) the Action Replay could keep a complete copy of the state of all those registers in its own internal memory. This state could then be saved, along with the contents of the computer's RAM for later re-loading. By pressing a button on the Action Replay, an interupt loaded a special monitor program from the Action Replay's ROM which could then be used to load, save and modify the computer's memory. It was even possible to alter CPU registers of the paused code, and later revisions included a complete disassembler. Cheating was possible by altering values stored in RAM.
A knob on the Amiga version of the Action Replay MKIII allowed games to be slowed down, to make them easier. This worked by intercepting vertical blank interrupts and running a wait loop until at least the next vertical blank. This did, however, have the limitation of only being able to reduce game speed by 50% or more.
The Action Replay was a formidable opponent for anyone trying to prevent their game code or graphics being ripped, or their game saved for later re-loading. One weakness was discovered in the Amiga version. It was possible to detect when the interrupt (hardware level 7, unmaskable) which the Action Replay used had been triggered, but only after the Action Replay monitor program had exited. At best the programmer could then choose to crash his program deliberately, making saved copies crash as well. However, it was possible to patch code which did this using the monitor program, so even that was not a total defense.
Later Action Replays which only supported cheat codes and had no monitor program worked by monitoring memory access for certain triggers, or by overwriting certain memory addresses at particular times (such as once per frame, or on a timer). On systems such as the Dreamcast, this could even be done entirely in software.