Various aspects of tape measures with one or more of a sensor, a motor, and a clutch, are shown. The sensors described herein detect, through various mechanisms, the position of the retraction system of a tape measure. The measurements by the sensors may be used to control a motor to adjust an amount of tension in the spiral spring of a tape measure. In various embodiments a motor interacts with the retraction system of the tape measure via a clutch, which moderates an amount of force that the motor can communicate to the retraction system.