An electrically-powered, wearable device (e.g., wristband, finger probe, head-worn sensor) designed to continuously measure and record: 1) photoplethysmography (PPG) data (e.g., pertaining to heart rate, respiration rate); and, 2) movement, during normal day- and/or night-time activities at home. It includes an optical PPG sensor and an accelerometer. The data is typically transferred to a local application or central database for analysis which includes evaluation of lifestyle factors (e.g., energy expenditure, activity level, sleep patterns).