A sensor apparatus for monitoring a vital sign of a subject comprises at least one sensor configured to measure a sensor signal representing a vital sign or being related to a vital sign, an evaluation unit configured to evaluate said sensor signal to determine, based on previously measured sensor signals, changes of the health condition of the subject and/or to identify an unsuccessful measurement or an unreliable sensor signal, and a control unit configured to control said at least one sensor to automatically change the measurement interval based the result of said evaluation.
