The "Memento Mortem" pocketwatch is a device that can be used to observe the moment of death of a person or an animal. As a prerequisite, the user must be near some remains of the deceased in order to use the watch.
The name "Memento Mortem" is Latin for "Remember Death", a variation of the saying "Memento Mori" ("remember that you will die").
Surgeon Henry Evans had the pocketwatch aboard the Obra Dinn in 1802 and took it with him when he left the ship by lifeboat. After hearing of the Obra Dinn's return to Falmouth five years later, Evans mailed the watch along with an enclosed catalogue to the East India Company in hopes that it would help to reveal the truth about the events on board.
An East India Company inspector used the watch to discover what had happened, and as requested by Evans, mailed the catalogue of the findings back to him, but the inspector was allowed to keep the watch.
Before his death, if the inspector had completed the rest of the catalogue, Evans sent back the book along with a paw of his pet monkey to the inspector. By using the pocketwatch on the paw, the inspector was able to piece together the final missing events on the ship.
The pocketwatch is retrieved from a case the inspector brings to the Obra Dinn in a rowboat. The boatman is unable to hoist it to the main deck, so the watch must be acquired by climbing back down to the rowboat.
The inspector pulls out the watch automatically when near a corpse. The hands on the watch will display the chapter and the part the corpse leads to. The hour hand displays the chapter number and the minute hand shows the part at five-minute intervals (e.g. 3:05 is chapter III, part 1; 3:10 is part 2, and so on). Interacting with a corpse/remains will transport to a memory: a frozen scene of the victim's moment of death.
While in a memory, the watch may start shaking to indicate a new corpse to be found within the memory that had been removed in the present reality. Upon discovering a corpse, the watch transports back to reality and sends forth a wisp to manifest the corpse in a noisy incorporeal image that the watch can be used upon. Eyesight and/or proximity of the wisp must be maintained to allow it to continue moving. The wisp is not always required, especially if the setting is no longer accessible.
Through this alteration of reality, the pocketwatch is also able to open certain doors/trapdoors and restore the lights/lamps: essentially "reproducing" the scene of a memory. This allows access to locked-off areas. Objects affected by the pocketwatch will have noise on them, just like the corpses from memories.