People's daily activity in their home has widespread implications, including health and energy consumption, yet in most environmental studies people’s activity is only estimated by using screening or structured observation. This paper reviews the current protocols and standards, and then identifies a mixed-method approach to measure people's activity levels in free-living environments. One of the key issues is to gather accurate measurements while using ‘discreet’ observatory methods to have minimum impact on their behaviour. With the recent emergence and advancement of more accurate and affordable sensing technologies, this problem might be overcome. Drawn from physiological research, heart-rate monitoring, accelerometry, and automated visual diary, were used in a field study, which monitored a small sample of UK households during the winter of 2012. Within a smart home, these methods could potentially be used to forecast energy demand for heating and to manage power distribution peaks.