Wearable Sleep Technology
The use of wearable sleep technology (i.e., devices worn on the body to measure aspects of sleep such as sleep/wake cycles) is increasing among consumers. Benefits of wearable sleep technology are that it collects information about a person's sleep in their natural environment and can record information over an extended period of time, compared to having a polysomnographic study in which the “first night effect” and having incomplete data in a sleep diary can negatively impact results. However, little guidance exists regarding how to use these devices effectively in clinical and nonclinical settings (e.g., sleep research, consumer market). In addition, scientists have concerns regarding the devices’ validity, accuracy and reliability in measuring various sleep parameters (e.g., sleep stages, sleep/wake cycles).
In 1978, Kripke and colleagues1 described an accelerometer-based wrist actigraph that measured sleep/wake cycles based on changes in a person’s general activity level between sleep (i.e., less active) and wake (i.e., more active). In their study, wrist actigraphy, electroencephalography (EEG), electrooculography (EOG) and electromyography (EMG) data were obtained simultaneously. They compared the total sleep time as measured with wrist actigraphy and manual scoring (based on EEG-EOG-EMG recordings). The correlation between wrist actigraphy and EEG-EOG-EMG with regard to minutes of sleep, total sleep period and minutes of wake during a sleep period was high at 98%, 95% and 85%, respectively. Based on these findings, Kripke suggested that continuous wrist activity recordings could provide very accurate estimates of sleep time.
Since then, wearable sleep-trackers have been developed in many forms: wristband, armband, smartwatch, headband, finger ring and sensor clip. Some popular manufacturers of consumer sleep technology (CST) devices and their products include:
- Fitbit, Inc. (San Francisco, CA): Charge 3-5, Charge HR, Versa and Versa 2-3
- ActiGraph Corporation (Pensacola, FL): GT9X Link and wGT3X
- Ōura Health Ltd. (Oulu, Finland): Smart Ring
- Apple, Inc. (Cupertino, CA): Apple Watch
Many CST devices purport to track a consumer’s sleep, provide sleep-related metrics (e.g., sleep architecture, sleep stages), improve sleep quality or screen for sleep disorders (e.g., obstructive sleep apnea [OSA], periodic leg movements). However, the extent that these claims are true when compared to objective data obtained with polysomnography (PSG) has shown conflicting results with regard to accuracy and reliability.
1. Kripke DF, Mullaney DJ, Messin S, et al. Wrist actigraphic measures of sleep and rhythms. Electroencephalography and Clinical Neurophysiology. 1978;44(5):674-676.