Each Night the Lie Detector sends the Moderator a post or statement made by another player, and the Moderator tells the Lie Detector whether that other player was telling the truth when they made that post.
A sample use of this power would be to find out whether a role claim is true or not. However, trying to use this ability on something that cannot be verified objectively (i.e. whether someone was telling the truth when they said that a wall of text was a waste of time) the moderator will likely just say "I don't know".
Lie Detectors tend to be Town, and also tend to be X-Shot.
Town-aligned Lie Detectors can easily translate themselves into Cops simply by forcing each player to say "I am aligned with the Town". Thus, they are not seen often at all.
Use and Power
Use a Cop instead.