Sleep mode is a standby feature that allows a platform to reserve power while still keeping the system on and the game's progress intact. Sleep mode has been present since the Game Boy Advance; however, only the Nintendo DS and up can go into sleep mode in any game. The Game Boy Advance requires a game that allows sleep mode. To put a Nintendo DS or 3DS system into sleep mode, simply close the system.
Game Boy Advance
The GameBoy Advance does not have a proper sleep mode. Instead, some games support a form of sleep mode that is accessed from a menu. The Game Boy Advance's sleep mode causes the screen and sound to shut off while still retaining the game's progress. The purpose of this is to augment the system's battery power. Getting the system out of sleep mode is a bit more complicated. To do so, the player has to press the L and R buttons at the same time and hold down select. After releasing these buttons, the system will turn back on. Because sleep mode is software-based, this works the same way with the Game Boy Advance SP, and the Game Boy Micro.
Sleep Mode glitch
Placing any type of magnet (including another Nintendo DS or 3DS system) near a Nintendo DS or 3DS system will put the system in sleep mode if it is open, or take it out if it is closed. Doing this can potentially cause permanent damage to the magnets on some systems.