The present invention relates to a device (16) and method for monitoring a physiological state of a subject (32). To reduce the energy consumption but still provide a high accuracy, the proposed device comprises a sensor interface (18) for obtaining from a sensor (20) a sensor signal indicative of a vital sign of a subject a power storage interface (22) for obtaining a charge value indicative of a charge state of a power storage (24) powering the sensor a duty cycle module (28) for controlling the duty cycle of the sensor based on the charge value and a processing unit (26) for extracting at least one feature indicative of a physiological state of the subject from the sensor signal.
