Lie Detection is the ability to intuitively sense, or sense through psychic vibrations, when another person is lying, even if the person the power is used on has a distorted perception of reality. It is largely a passive ability, being uncontrolled by the possessor. The ability can only detect lies, not false statements in general. It is unknown whether the ability works on a physiological level or a mental level.
Sue is able to detect Sylar's lie immediately after she is told he's there to make a delivery. Sylar also remarks that her ability must be a burden to her, which suggests that Sue had no control over her ability.