Key to the Dead Man's Chest

The Dead Man's Chest that holds the heart of Davy Jones cannot be opened without the Key. At the beginning of Dead Man's Chest, Jack Sparrow escapes from a Turkish prison with a drawing of the key. He knows that he wants to find both the Key and the Chest that it opens, but he isn't quite sure where to find either, as his compass isn't working properly for him. He manages to turn Will Turner's desire to save Elizabeth Swann from execution into a way to search for the Key. The Vodou priestess Tia Dalma tells them the story of Davy Jones' heart, and that he has hidden the chest and keeps the Key on him at all times. Will rounds on Jack angrily, saying, "You knew this." Jack denies this, but says all they need to do now is find the Flying Dutchman, steal the key, find the chest and take it back to Port Royal to save Elizabeth. Tia Dalma at this time gives Jack a large Jar of Dirt to protect him from Davy Jones before she reveals to them the location of the Flying Dutchman. 

Onboard the Flying Dutchman
Jack betrays Will, tricking him into Davy Jones' crew. Will meets his father, is told by Wyvern that if he stabs the heart inside the Chest, all the souls aboard the Flying Dutchman will go free. Will challenges Jones to a game of Liar's Dice in an attempt to find out where the Key is hidden. Will steals the Key from Davy Jones while he sleeps. Will escapes to the Edinburgh Trader, which is destroyed by the Kraken. 

On Isla Cruces
Will stows back aboard the Flying Dutchman for the ride to Isla Cruces, where he confronts Jack, who has just dug up the Dead Man's Chest. A three-way fight for the Key begins between Will, Jack, and James Norrington. Jack gains the key, but is disarmed. He then manipulates Norrington into attacking Will and escapes with the Key and his sword. After escaping the downhill fight in the water will, Jack opens the Dead Man's Chest, removes Jones' heart, and leaves the key in the lock of the empty chest, making it appear unopened. 

Last Sighting
The last appearance of the Key is on the Flying Dutchman after Jones' crewmen have regained the (empty) chest and taken it aboard. After the Kraken has dragged the Black Pearl back to the depths with Jack Sparrow still aboard, Davy Jones decides he should check the Chest, just to make sure. He uses the Key to open the Chest and find it empty. Our last sight of Jones is of him shouting to the heavens, "Damn you, Jack Sparrow!"