(3 Point Merit)
You are skilled in picking up the minute signs of people lying. You know to watch which way they look, to time how long they hesitate, to read the tone of their voice... No lie slips past you that isn't supernaturally bolstered.
In game terms, any attempt to detect all but the most serious lies succeeds automatically. If the lie being detected is of a serious nature (it contains plot information, or could lead to character death/meaningful consequence, etc.), or the liar is using supernatural means to bolster their persuasiveness (i.e. Persuasion, etc) you instead receive a -2 difficulty to detect the lie. If you are attempting to detect a lie from a character with the Merit: Perfect Liar, roll as normal (neither the liar nor the lie detector receive any bonuses).