Apple Watch: Deep Sleep Tracking Explained

The Apple Watch is a useful device for tracking sleep. It can monitor sleep patterns and provide insights into sleep quality. To use the Apple Watch for sleep tracking, users need to wear the watch to bed and ensure it is charged to at least 30% before sleep. The watch can then estimate the time spent in each sleep stage, including REM, Core, and Deep sleep, as well as the number of times the wearer wakes up throughout the night. This data can be viewed in the Sleep app on the Apple Watch or the Health app on the iPhone. Additionally, the Apple Watch can also track the wearer's heart rate, respiratory rate, and wrist temperature, providing further insights into their overall health and sleep quality. While the Apple Watch provides basic sleep tracking features, some users may prefer to use third-party apps for more detailed insights.

Apple Watch's sleep tracking feature

The Apple Watch's sleep tracking feature allows users to track their sleep and monitor their sleep patterns. The watch uses signals from the built-in accelerometer and heart rate sensor to detect movement and keep a check on sleep stages. This includes the time spent in REM, Core, and Deep Sleep, as well as the number of times the wearer wakes up during the night. The Apple Watch can also track the wearer's breathing rate, heart rate, and blood oxygen level, which can provide insights into respiratory health and potential sleep disorders such as sleep apnea.

To use the sleep tracking feature, users need to enable sleep tracking and set a sleep schedule. This can be done through the Health app on the iPhone or directly on the Apple Watch. Users can set sleep goals, bedtime and wake-up times, and even create multiple sleep schedules, such as one for weekdays and another for weekends. The Sleep app on the Apple Watch will then provide information about the amount of sleep the wearer got, the time spent in each sleep stage, and their sleep average over the past 14 days.

It is important to note that the Apple Watch does not automatically track sleep and requires the user to wear it to bed. Additionally, while the sleep tracking feature provides insights into sleep patterns, it should not be solely relied upon for sleep analysis as it may not provide the same range and accuracy of data as clinical sleep studies. However, it can be a useful tool for regulating sleep time and improving overall health and well-being.

Third-party sleep tracking apps are also available for the Apple Watch, offering additional features such as in-depth sleep analysis, smart alarm clock functions, and more detailed data on sleep cycles.

Heart rate and motion sensors

The Apple Watch uses a combination of heart rate and motion sensors to track an individual's sleep. The watch's accelerometer and heart rate sensor detect movement and keep a check on sleep stages. This technology is called Photoplethysmography (PPG) and is used to measure the wearer's heart rate. The combination of motion and heart rate data is used to develop algorithms that approximate the brainwaves detected by electrode sensors. By analyzing these brainwaves and physiological states, the Apple Watch can estimate an individual's sleep stage with about 80% accuracy.

The Apple Watch can differentiate between REM, Core, and Deep sleep stages. REM sleep, indicated by a light blue dot, is when the wearer is dreaming. Core sleep, indicated by a blue dot, represents a light sleep stage. Deep Sleep, indicated by an indigo blue dot, is a restorative phase for the body and mind. The watch also shows an orange dot, representing the amount of time the wearer is awake at night.

In addition to sleep stages, the Apple Watch also provides sleep duration details such as Average Time in Bed and Average Time Asleep. This data can be compared with the wearer's heart rate and respiratory rate to gain deeper insights into their sleep health. For example, the Apple Watch can monitor breathing metrics, heart rate, and heart rate variability, which could indicate potential problems such as sleep apnea.

The Sleep app on the Apple Watch allows users to set up personalized sleep schedules, including sleep goals, bedtime, and wake-up times. It is important to note that sleep tracking on the Apple Watch requires the device to be worn to bed and charged to at least 30% before sleep.

Sleep schedules and goals

The Apple Watch has a built-in sleep tracker that can help you create sleep schedules and set goals to improve your overall health. To access the sleep tracking feature, open the Sleep app on your Apple Watch or the Health app on your iPhone.

To set up a sleep schedule, tap "Add Schedule" in the Sleep app. You can also create multiple sleep schedules, such as one for weekdays and another for weekends. For each schedule, you can set a wake-up time, bedtime, sleep goal, wind-down time, and alarm options. The Sleep app will suggest a bedtime based on your wake-up time and sleep goal. You can also adjust your wind-down and sleep goal as needed.

The Sleep app will track your sleep duration, the time spent in each sleep stage (REM, Core, and Deep), and your sleep trends over the past 14 days. It is important to note that you need to pre-define your sleep schedule within the app for accurate tracking. Additionally, make sure your Apple Watch is charged to at least 30% before bed to enable sleep tracking.

By utilizing the sleep tracking feature on your Apple Watch, you can gain insights into your sleep patterns, identify areas for improvement, and make informed decisions to optimize your sleep quality and overall health.

Sleep tracking accuracy

The Apple Watch uses signals from the accelerometer and heart rate sensor to detect when users are in REM, Core, or Deep sleep. It can also measure and track the user's Respiratory Rate. However, the accuracy of the Apple Watch's sleep tracking feature has been questioned by some users.

Some users have reported that the Apple Watch records significantly less deep sleep compared to other sleep tracking devices and applications, such as Fitbit, Garmin, Polar, and AutoSleep. For example, in one instance, the Apple Watch recorded only 7 minutes of deep sleep, while a Xiaomi Band 7 recorded 1 hour to 1 hour 40 minutes. Similarly, another user reported that the Apple Watch recorded 12 minutes of deep sleep, while a FitBit recorded 1 hour 33 minutes. These discrepancies have led some users to question the accuracy of the Apple Watch's sleep tracking feature.

However, it is important to note that the accuracy of sleep tracking devices can vary depending on various factors, such as the algorithms used, the type of device, and individual differences. A study published in PMC compared the accuracy of 11 different consumer sleep trackers (CSTs), including the Apple Watch 8, and found that they exhibited diverse performances across sleep stages. The Apple Watch 8 was reported to use alternative expressions for sleep stages, such as “core sleep” instead of light sleep. Additionally, the study found that wearables, like the Apple Watch, showed high proportional bias in sleep efficiency.

Despite the discrepancies in recorded sleep data, some experts have supported the accuracy of the Apple Watch's sleep tracking. Dr. Dan Gartenberg, a sleep scientist and CEO of SleepSpace, stated that devices like the Apple Watch use Photoplethysmography (PPG) to measure heart rate and, combined with motion data, can develop algorithms that estimate brainwaves with about 80% accuracy. He added that these tools provide valuable insights into sleep health since healthy sleep is characterized by more REM and deep sleep.

While the Apple Watch may not provide perfect accuracy, it can still be a useful tool for monitoring sleep patterns and trends over time. Additionally, it is important to consider one's subjective experience of sleep quality, as suggested by Dr. Valerie Cacho, a sleep medicine specialist. She recommends that individuals should not solely rely on the data provided by sleep tracking devices and should also consider how they feel in the morning as a measure of their sleep quality.

Third-party sleep tracking apps

While the Apple Watch can track sleep, many users have turned to third-party apps to supplement the Sleep app and collect more detailed information. Some of the most popular third-party sleep tracking apps include:

• AutoSleep: This app integrates seamlessly with Apple Health and mirrors Apple's activity rings. It tracks sleep duration and quality and uses this data to determine how prepared you are for the day.
• Sleep++: Sleep++ provides data-driven sleep tracking that shows how many times you enter deep sleep per night.
• Pillow: Pillow offers in-depth sleep analysis and a smart alarm clock function that wakes you up at the optimal time for maximum refreshment.
• SleepWatch: SleepWatch allows users to swipe between different sleep detection algorithms.
• Napbot
• BetterSleep
• Sleep Cycle
• ShutEye

These third-party apps can provide more detailed insights into your sleep patterns and help you make more informed decisions about your sleep habits. However, it's important to note that while these apps can be useful tools, they may not provide the same level of accuracy as clinical sleep studies, which use a variety of data-gathering technologies. Additionally, over-tracking sleep can lead to ortho insomnia, so it's important to balance the use of these tools with your subjective experience of sleep quality.

Frequently asked questions