A combined detectional and positional sensor for a syringe pump. The sensor can comprise a syringe thumbpress clamp that is pivotable so that an engagement pin deflects a linear membrane potentiometer first circuit thus providing a closed switch for detection of a syringe in the pump and a variable signal return for indication of plunger head position. Embodiments of the sensor can be used in relatively large syringe pumps and in relatively small syringe pumps, for example.