Various embodiments relate to apparatuses and methods of using light transmission thought living tissue, such as a finger, to detect the flexure of a joint. Light is introduced into the tissue at one point, passes through the tissue, and exits the tissue at a second point where a sensor receives the light as it exits the tissue. Transmission of light through living tissue such as a finger can be affected by movement of the finger. As the finger flexes and, for example, the joints of the finger change angle, the characteristics of the light exiting the tissue, such as the intensity of the light, can change. These changes in characteristics can be used as an indirect means of determining the flexure of the joint.