This study evaluates the accuracy of five commercial sleep-tracking devices compared to research-grade actigraphy and polysomnography (PSG) in monitoring the overnight sleep of 53 young adults. The devices included the Fitbit Inspire HR, Fitbit Versa 2, Garmin Vivosmart 4, Withings Sleep Tracking Mat, and Oura Ring Gen 2. The study assessed biases and limits of agreement between the devices and PSG for total sleep time, wake after sleep onset, light sleep, deep sleep, and REM sleep. Results showed that all devices, except the Garmin Vivosmart, estimated total sleep time comparably to research-grade actigraphy. However, all devices overestimated nights with shorter wake times and underestimated nights with longer wake times. For light sleep, the Fitbit Inspire and Fitbit Versa had low absolute 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. Overall, the findings suggest that consumer sleep-tracking technologies exhibit prevalent proportional bias patterns, which could impact their overall accuracy. The study highlights the need for further research to improve the reliability and accuracy of these devices.This study evaluates the accuracy of five commercial sleep-tracking devices compared to research-grade actigraphy and polysomnography (PSG) in monitoring the overnight sleep of 53 young adults. The devices included the Fitbit Inspire HR, Fitbit Versa 2, Garmin Vivosmart 4, Withings Sleep Tracking Mat, and Oura Ring Gen 2. The study assessed biases and limits of agreement between the devices and PSG for total sleep time, wake after sleep onset, light sleep, deep sleep, and REM sleep. Results showed that all devices, except the Garmin Vivosmart, estimated total sleep time comparably to research-grade actigraphy. However, all devices overestimated nights with shorter wake times and underestimated nights with longer wake times. For light sleep, the Fitbit Inspire and Fitbit Versa had low absolute 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. Overall, the findings suggest that consumer sleep-tracking technologies exhibit prevalent proportional bias patterns, which could impact their overall accuracy. The study highlights the need for further research to improve the reliability and accuracy of these devices.