1. A system configured to reduce power consumption of a wearable device comprising a sensor, by utilizing eye tracking, comprising: a gaze analyzer configured to receive first and second eye tracking data of a user acquired essentially during exposure of the user to respective first and second segments of content presented on a display that is not part of the wearable device; the gaze analyzer is further configured to determine from the first eye tracking data that a gaze-based attention level to the first segment reaches a first predetermined threshold; the gaze analyzer is further configured to determine from the second eye tracking data that a gaze-based attention level to the second segment does not reach a second predetermined threshold, and to indicate an indication thereof to a mode-selector; and the mode-selector is configured to operate the wearable device in a first mode of operation to measure, utilizing the sensor, affective response of the user to the first segment, and responsive to the indication, to operate the wearable device in a second mode of operation to measure, utilizing the sensor, affective response of the user to the second segment; wherein, when operating in the second mode of operation, power consumed by the wearable device for measuring affective response is significantly lower than the power consumed by the wearable device for measuring affective response when operating in the first mode of operation.