Signed: Joe Hill
First appearance: Guide to the Known Keys (one-shot)
Use: Allows someone to become a ghost
Door: Ghost Door
The Ghost Key allows the user to become a ghost when they pass through the Ghost Door.
The ghost seems to be a representation of the individual’s soul; when the infected soul of Lucas Caravaggio passed through the door, the demon could be seen “attached” to his ghost. The ghost may not be seen or heard, except by other ghosts, or by Rufus Whedon. Ghosts can see and hear, however, and can therefore gain information with it.
Ghosts can teleport to people they think about, or may be summoned when other people think about them. The ghost itself is confined to Keyhouse.
Ghosts can alter their appearance to some extent. Dodge was able to change his ghost’s gender, and Sam Lesser was able to “dress” his ghost in military equipment. Both ghosts were able to manifest weapons when they fought, Dodge using a fencing sabre and Sam using a chainsaw.
When more than one ghost enters the same body, they can attempt to wrestle control over the body from each other.
To return to “life”, the ghost simply needs to return through the Ghost Door. They will wake up in their body, even if their body has been moved. If there is no living, “empty” body to enter, the person may be stranded as a ghost.
The Ghost Door is an exterior-facing door located in the winter study on the East side of Keyhouse. The Ghost Door is “activated” by using the Ghost Key first, after which multiple people may become ghosts.
Source: Locke & Key Wikia