Miya Pearson
Sleep tracking is a feature of the Fitbit Flex, which automatically recognises when you are sleeping and logs your sleep. The Fitbit Flex uses an accelerometer to measure bodily accelerations of the wrist and optical photoplethysmography (PPG) to measure blood flow based on how green light from an LED on the back of the watch is reflected by the body. It also uses heart rate and movement to infer whether you are awake, in a deep sleep, a light slumber, or dreaming. Fitbit devices that track heart rate also track sleep stages.
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What You'll Learn
Fitbit Flex's auto sleep tracking
Fitbit Flex's auto sleep-tracking feature was released in 2015. It automatically recognises when you're sleeping and logs your sleep for you. There is no need to manually activate sleep mode. The tracker uses your movement and heart-rate patterns to estimate your sleep stages. When you don't move for about an hour, your Fitbit Flex assumes you're asleep. Additional data, such as the length of time when your movements indicate sleep behaviour (like rolling over), help confirm your sleep status.
While you sleep, your Fitbit Flex tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, it uses your movement and heart rate patterns to estimate your sleep cycles from the previous night.
Fitbit's sleep researchers and the National Sleep Foundation describe the following sleep stages:
- Light sleep: Your entry point into sleep each night as your body unwinds and slows down.
- Deep sleep: A stage of sleep with less brain activity than REM sleep.
- REM sleep: The stage associated with vivid dreams, and the stage when a person is most likely to be dreaming. Periods of REM sleep are typically longer as the night goes on.
To be eligible for a sleep profile, you must meet certain requirements. These include having a Fitbit Premium subscription and using a compatible device. You must also wear your Fitbit during sleep for at least 14 days during the previous month.
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How to set up sleep tracking
To set up sleep tracking on your Fitbit, you will need to open the Fitbit app on your phone. From the Today tab, tap the "Sleep duration" tile. Tap the menu icon at the top right, then tap "Settings". Tap "Sleep", Bedtime, Wake Time, or Sleep duration to set or edit your targets. You can also get to this menu by hitting the gear-like Settings icon at the top left of your app's Sleep menu.
You can also set a sleep goal. Open the Fitbit app on your phone. Tap on the round icon that may (or may not) have your photo, at the top left of the screen. Tap "Activity and Wellness" > "Sleep" > "Time Asleep Goal", and use the pull-down menu to adjust your total sleep target.
You can also set a bedtime reminder in the Fitbit app to help you maintain a consistent sleep schedule. When it's time to wind down for bed, you will receive a notification on your phone. On certain Fitbit devices, you can also find a bedtime reminder on your device.
To check your sleep data, sync your device each morning. You can then check your sleep data on your Fitbit device or in the Fitbit app. You can check your averages for the week or longer periods of time for certain sleep stats, including hours slept, sleep score, sleep schedule, and sleep stages.
Please note that some features, such as the snore and noise detection feature, are only available with a Fitbit Premium subscription.
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Sleep tracking data and insights
Fitbit's sleep-tracking function works by automatically detecting when you're sleeping and logging your sleep for you. It does this by using an accelerometer, which measures bodily accelerations of the wrist, and optical photoplethysmography (PPG), which measures blood flow based on how green light from an LED on the back of the watch is reflected by the body. It also uses your heart rate and movement patterns to determine when you're asleep. When your body is completely at rest and hasn't moved for about an hour, your device records that you're asleep.
The Fitbit app provides a range of data and insights about your sleep, including:
- Sleep schedule: An overview of your sleep schedule for the week, including bedtime and wake-up times.
- Sleep stages: The number of hours spent in each sleep stage (light sleep, deep sleep, and REM sleep) and your weekly average minutes asleep. Fitbit devices that track heart rate can provide more accurate data on sleep stages.
- Sleep score: A personalized score based on heart rate, restlessness, and other metrics.
- Sleep trends: View trends in your sleep data over time and compare your stats to others.
- Sleep profile: A monthly personalized analysis of 10 key metrics to help you improve your sleep habits and quality. This feature requires a Fitbit Premium subscription.
- Snore and noise detection: With a Premium subscription, you can enable this feature to allow the microphone on your Fitbit Sense or Versa 3 to track noise, including snoring from you or someone next to you.
- Smart Wake: This feature monitors your sleep stages and wakes you during a light sleep stage within a 30-minute window before your set alarm time.
It's important to note that sleep cycles vary naturally, so your sleep data may occasionally fall outside the typical ranges. Additionally, some users have reported frustrations with certain features, such as the SpO2 sensor, which is not currently used by the Fitbit app despite its potential to provide valuable feedback to sleepers with sleep apnea.
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Sleep tracking with a Fitbit Premium subscription
To use sleep tracking with a Fitbit Premium subscription, you must meet certain requirements. These include having a compatible device, such as the Charge 5, Inspire series, Luxe, Pixel Watch series, Sense series, or Versa series. Additionally, you need to wear your Fitbit during sleep for at least 14 days in the previous month, and your sleep logs must include sleep stages data.
With a Fitbit Premium subscription, you can access features like snore and noise detection, which uses the microphone on your device to track snoring or other noises during the night. You can also review your sleep data each morning by syncing your device to the Fitbit app. This data includes your sleep score, hours slept, sleep schedule, and sleep stages.
The Fitbit Premium Sleep Profile assigns you a "sleep animal" out of six options, representing different sleep styles. This feature takes into account various factors, such as the time until you fall into a deep sleep, your regular bedtime, the number of days with naps, and the total time spent in deep sleep. Your sleep animal may change from month to month, reflecting the dynamic nature of your sleep habits.
While some users have found the Fitbit Premium sleep tracking features insightful and helpful for improving their sleep, others have expressed concerns about the accuracy and cost of the service. Ultimately, the decision to subscribe to Fitbit Premium for sleep tracking depends on your specific needs and preferences.
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Sleep tracking accuracy
The accuracy of sleep-tracking in the Fitbit Flex is questionable. While Fitbit claims that its sleep-tracking features work as promised, many experts have raised concerns about the accuracy of sleep-tracking fitness devices in general.
Fitbit Flex uses automatic sleep tracking to recognize when you are sleeping and logs your sleep for you. It does this by detecting when your body is completely at rest and you haven't moved for about an hour. It also uses your movement and heart rate patterns to estimate your sleep cycles and the stages of sleep you are in (REM, deep sleep, and light sleep). Fitbit's sleep stages are based on research done in collaboration with sleep researchers from the National Sleep Foundation.
However, critics have pointed out that fitness trackers depend too heavily on users' movements to determine sleep levels, lack transparency in their sleep-tracking algorithms, and tend to reinforce bad sleep habits by encouraging extended time in bed. Experts are also skeptical about the ability of fitness trackers to accurately track sleep stages, as these devices rely on movements while sleep stages are primarily defined by brain activity. The algorithms used to calculate sleep are not transparent, making it difficult to determine their accuracy.
Some users have expressed satisfaction with the sleep-tracking features of Fitbit devices, finding them neat and accurate. However, others have been disappointed, finding inconsistencies in the data and missing sleep stage information.
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Frequently asked questions
Fitbit Flex automatically recognises when you're sleeping and logs your sleep. It uses your movement and heart-rate patterns to estimate your sleep stages. When you don't move for about an hour, your tracker assumes you're asleep.
To set up sleep tracking, wear your Fitbit Flex to bed. It is recommended that you wear your device in a snug wristband during sleep.
You can check your sleep data on the Fitbit app. Sync your device each morning to review your sleep data, such as your sleep score.
