A sensor guide wire device (200) for intravascular measurements of a physiological variable in a living body is disclosed. The sensor guide wire (200) may comprise a sensor element (213) and a connector unit (220). The connector unit (220) is attachable to a signal converting device (310). The sensor element (213) provides the signal converting device (310) with a signal indicative of a physiological variable sensed by the sensor element (213). Furthermore, the connector unit (220) comprises a battery (222). A system (300) comprising the sensor guide wire device (200) and the signal converting device (310) is also disclosed.