An optical vital signs sensor is provided which comprises at least one light source with a primary and a secondary light unit and a photo detector, a motion sensor configured to detect a motion of a user, a periodicity metric unit to analyze an output signal of the at least one motion sensor to detect a periodicity in its output signal and a control unit configured to control an operation of the at least one primary and secondary light unit and to activate the at least one secondary light unit in addition to the at least one primary light unit when the periodicity metric unit does not detect a periodicity in the output signal of the motion sensor.
