When playing Metal Gear Solid 2 or Metal Gear Solid 3, if you are spotted or go into Alert mode (none that are part of the story line, three for Metal Gear Solid 3 which will be noted at the end of the game), save the game. Once saved, do an in-game reset. Load the game. You will resume from the last point you were without any alerts. This is very useful when trying to earn the "Complete Stealth" achievement or trophy for Metal Gear Solid 2 and the "Stealth Camouflage" achievement or trophy for Metal Gear Solid 3. You will receive the bonus for "No Alerts" at the end of the game.
Snake and Raiden wearing sunglasses
Successfully complete the game two times, then start a New Game+ session.