This paper discusses the technology of polygraph machines and lie detector tests in relation to the body as a specific site of truth investments. It discusses the way the machine is imagined or constituted in popular culture and scientific literature as a means of discovering guilty knowledge or getting the truth objectively and painlessly. It argues that the history of this technology turns truth or the sign of concealed knowledge into a bodily manifestation that is graphically capturable and ultimately readable. The graphic tracings multiply the scene or site of confession from a voluntary or involuntary verbal process to a bodily one. This technology does not operate on a model of truth represented through the body, where it is imagined as hidden within the interior of the body an interior that houses or contains secrets. On the contrary, whether for better or worse, this technology constitutes truth or the sign of deception as an animate, graphic sign in and through a body that speaks. Breathing patterns, pulse rates and secretions of sweat are constituted as meaningful, and this opens the way for potentially limitless decipherability.