Finger and Wrist Wearables for Tracking Sleep

Every sleep-tracking device that fits on the fingers or wrists can’t read brain waves. Instead, they take indirect clues such as movement, blood flow, and skin temperature to make an educated guess about brain waves. Since wearables can’t register EEG electrical signals, they use optical sensors to track blood flow and micromovements. However, if one is lying still with a plummeting pulse, the algorithm might incorrectly assume the individual is in deep sleep. As a result,  accuracy varies and their estimates cannot always be trusted. Although wearables are more accurate estimating awake vs. asleep, their categorization of sleep into four stages—awake, light, REM (or rapid eye movement) and deep sleep—use proxy data that is subject to errors that might prompt users to alter habits or medications. A 2025 study published in Nature showed that the Oura ring was only 53% accurate compared to EEG-based laboratory sleep studies in identifying sleep stages. For these reasons,  most sleep experts agree that it is the perception of sleep that is most important in insomnia.