The Tablet of Ahkmenrah was Ahkmenrah's most prized possession. It was given to him by his father so that the family may 'live on past death together.'
The Tablet was a creation of Merenkahre and his servants to be a gift for Ahkmenrah. It's powers can be restored in the light of the full moon as it's connection to the Egyptian Moon God Khonshu.
In the 1950s, the Museum acquired the tablet from the temple of the Pharoah. The tablet has the power to bring all of the exhibits, whether human or animal, to life during the night, but they must return to their places at sunrise. Anyone or anything who is outside of the Museum after the sun rises will turn to dust. It's one of the night watchman's duties to make sure that no one (or thing) gets in or out of the Museum. In the sequel, it is revealed reviving dead or inanimate objects is one of the tablet's powers and can be used to open a Gateway to the Underworld since its secondary function is a keypad.
Night at the Museum
In the first film, Teddy Roosevelt shows Larry the tablet on his first night as a night guard. He explains to Larry that it has made everything in the museum come to life every night ever since it was placed there. Nights later, Larry shows his son, Nick, the museum at night and how everything comes to life, but nothings happens. Larry then finds out that the tablet has been stolen by Cecil and the other guards and rushes off with Nick to retrieve it.
Night at the Museum: Battle of the Smithsonian
Two years later, many of the exhibits are being shipped to the Smithsonian as archives as the museum being upgraded by holograms of them. Dexter secretly takes the tablet with them, not wanting to be a nonliving museum archive exhibit. As a result, the tablet brings the entire Smithsonian Museum to life. Larry travels to D.C. to retrieve the tablet and does battle with Ahkmenrah's older brother, Kahmunrah.
Discovering the combination on the tablet has been changed, Kahmunrah coerces Larry Daley into finding out the new combination by trapping his cowboy friend Jedediah in an hourglass. He later learns the combination after Al Capone interrogates a bobble-headed Albert Einstein (it's pi), and uses it to open to the gate to Duat (the Egyptian underworld), unleashing an army of falcon-headed warriors. These are sent back to the underworld by the Abraham Lincoln Statue. Using the tablet's power, Larry opens banishes Kahmunrah into Duat and closes the door.
Night at the Museum: Secret of the Tomb
The tablet is shown to be corroding, as revealed by Ahkmenrah to Larry. When it corrodes, the exhibits completely forget everything temporarily, and begin to turn into their exhibit forms as they would during the day. As a result, they infiltrate the London Museum at night to find out how to restore it.
It is later revealed by Ahkmenrah's parents Merenkahre and Shepseheret that it needs moonlight to restore itself. Shortly after realizing this, Sir Lancelot believes it is thee Holy Grail, and steals it from the main group, setting out for Camelot, which is revealed to be just a play. After cornering Lancelot, it is almost too late, as the tablet completely corrodes, they are almost in their day forms, and Dexter temporarily dies. However, eventually, after finally receiving it, Larry shines it in the moonlight, restoring the tablet and having the exhibits return to normal. They eventually decide to bring it to the London Museum to have it stay in it's normal condition forever. The Tablet of Ahkmenrah is later shown in Tilly's possession during a special traveling tour that she is overseeing and shows Dr. McPhee it's magic with the exhibits coming to life.