The KnowNow-measurement obtains information about children’s individual energy and activity levels. Our target of interest is to know how energetic does a child feels in differing environments, in school, home, hobbies, and friends. The individual energy level observations and interpretations are based on data gained through various subjective and objective measurements using a KnowNow-measuring device/sensor. The device/sensor is used similarly to a wristwatch. The KnowNow sensor/device is very accurate and recognizes even the tiniest of movements. The device/sensor can identify sleeping time and passive moments (i.e., sitting and screen time) but also distinct forms and levels of physical activity.