Sleep is a vital physiological process critically implicated in maintaining physical and mental health. Novel consumer-grade devices provide the op-portunity of tracking sleep, but their use for clinical and research purposes is limited due to lack of validation. This study aimed to validate sleep track-ing in free-living conditions by comparing total sleep duration measured by popular wearable devices with sleep diaries. Twenty-seven heathy volun-teers of median (interquartile range) age 21.0 (20.5-22.5), 71% male, and with wide range of skin tones (Fitzpatrick scale from 1 to 6) wore 5 devices for 2 consecutive nights and provided sleep diaries. Devices included the Garmin Vivoactive 4 (GV) and 4S (GVs), Fitbit Sense (FS), Withings Scanwatch (WS), and the Oura Ring (OR), which measured sleep duration using a standard and a β-software. Each night was considered as an inde-pendent observation. Agreement was assessed using the Spearman's correla-tion coefficients, average percentage error and Bland Altman plots. All de-vices expect WS reported some connectivity issues resulting in a maximum of 17 (GV) lost observations. 5% of GVs and 2% of FS estimates were con-sidered outliers (error >q3+1.5x(q3-q1) or