This study evaluates the accuracy of five commercial sleep-tracking devices compared to research-grade actigraphy and polysomnography (PSG) in measuring sleep stages and total sleep time in 53 young adults. The devices tested were Fitbit Inspire, Fitbit Versa, Garmin Vivosmart, Oura Ring, and Withings Mat. The study found that all devices except the Garmin Vivosmart were able to estimate total sleep time with comparable accuracy to research-grade actigraphy. However, all devices showed proportional bias, overestimating nights with shorter wake times and underestimating nights with longer wake times. For light sleep, the Fitbit Inspire and Fitbit Versa had low bias, while the Withings Mat and Garmin Vivosmart overestimated shorter light sleep and underestimated longer light sleep. The Oura Ring underestimated light sleep of any duration. For deep sleep, the Withings Mat and Garmin Vivosmart had low bias, while other devices overestimated shorter and underestimated longer times. For REM sleep, all devices had low bias. The study highlights the prevalence of proportional bias in consumer sleep-tracking technologies, which could affect their overall accuracy. The results suggest that while these devices can provide useful sleep data, they may not be as accurate as PSG or research-grade actigraphy. The study also notes that the accuracy of sleep staging varies depending on the device, sleep stage, and individual. The findings emphasize the need for further research to improve the accuracy and reliability of consumer sleep-tracking devices.This study evaluates the accuracy of five commercial sleep-tracking devices compared to research-grade actigraphy and polysomnography (PSG) in measuring sleep stages and total sleep time in 53 young adults. The devices tested were Fitbit Inspire, Fitbit Versa, Garmin Vivosmart, Oura Ring, and Withings Mat. The study found that all devices except the Garmin Vivosmart were able to estimate total sleep time with comparable accuracy to research-grade actigraphy. However, all devices showed proportional bias, overestimating nights with shorter wake times and underestimating nights with longer wake times. For light sleep, the Fitbit Inspire and Fitbit Versa had low bias, while the Withings Mat and Garmin Vivosmart overestimated shorter light sleep and underestimated longer light sleep. The Oura Ring underestimated light sleep of any duration. For deep sleep, the Withings Mat and Garmin Vivosmart had low bias, while other devices overestimated shorter and underestimated longer times. For REM sleep, all devices had low bias. The study highlights the prevalence of proportional bias in consumer sleep-tracking technologies, which could affect their overall accuracy. The results suggest that while these devices can provide useful sleep data, they may not be as accurate as PSG or research-grade actigraphy. The study also notes that the accuracy of sleep staging varies depending on the device, sleep stage, and individual. The findings emphasize the need for further research to improve the accuracy and reliability of consumer sleep-tracking devices.