How Accurate is Apple Watch Sleep Tracker?


In the realm of wearable technology, the Apple Watch has distinguished itself as a multifunctional device that not only aids in daily communication and fitness tracking but also ventures into the domain of health monitoring, with sleep tracking being one of its notable features. This article delves into the accuracy of the Apple Watch’s sleep tracker, evaluating its capabilities and limitations through a lens of scientific scrutiny and technological analysis.


The pursuit of understanding and improving sleep quality has led to a surge in the popularity of wearable sleep trackers. Among these, the Apple Watch has garnered attention for its sleep-tracking feature, promising users insights into their sleep patterns and quality. However, its accuracy is critical, as it underpins the reliability of the data provided to users, influencing lifestyle and health decisions. Luckily, studies have been published to help us better understand how the Apple Watch compares to clinically validated polysomnography devices.

Polysomnography, a clinically validated device, is the gold standard for diagnosing sleep disorders. It monitors various physiological functions during sleep through sensors, providing comprehensive data on the patient’s sleep patterns, stages, and disturbances. The device utilizes electroencephalography (EEG) to measure brain wave activity, which is essential for identifying sleep stages. Electromyography (EMG) sensors are employed to monitor muscle activity, including in the limbs to detect movements and in the chin to assess REM sleep characteristics. Electrooculography (EOG) tracks eye movements, which is critical for distinguishing REM from non-REM sleep stages. Respiratory effort and airflow are measured to detect sleep apnea using sensors around the chest and abdomen and a nasal cannula or thermistor.

Additionally, oxygen saturation is monitored via pulse oximetry, and heart rate and rhythm are assessed with electrocardiography (ECG). Together, these sensors provide a multidimensional view of sleep, allowing for precise diagnosis and tailored treatment plans.

The Science Behind Sleep Tracking

To evaluate the accuracy of the Apple Watch sleep tracker, it’s essential to understand the principles it relies on. The device uses a combination of motion detection (via an accelerometer) and heart rate monitoring to infer sleep stages. It primarily identifies periods of rest based on minimal movement and changes in heart rate, distinguishing between light and deep sleep phases.

To better understand how the Apple Watch tracks sleep, we first have to understand that the sleeping tracking features took time to be introduced to the Apple Watch ecosystem.

The sleep-tracking feature on Apple Watch Series 3 was initially launched in 2020 with iOS 14 and watchOS 7, allowing users to track their sleep by detecting two states – asleep or awake – in each 30-second analysis window. However, a more advanced version of the feature was released in 2022, along with iOS 16 and watchOS 9, which can now detect four states: Awake, Deep sleep, Core sleep, and REM (rapid eye movement) sleep. This improvement has enhanced the accuracy of the feature, making it more effective in tracking and analyzing sleep patterns.

Accuracy in Detecting Sleep Stages

Researchers debate the effectiveness of wearable sleep trackers in detecting sleep stages. These devices, such as the Apple Watch, are proficient in identifying when a person is asleep or awake. However, their ability to differentiate between different sleep stages—REM, light, and deep sleep—is not always reliable. 

This inconsistency arises because these devices rely on motion and heart rate as indicators of sleep stage, which are not direct measures of brain activity. This limitation makes it difficult to classify sleep stages accurately. As a result, while these devices can provide users with a general idea of their sleep patterns, the analysis is superficial as it lacks the precision needed for detailed assessment.

Impact on Sleep Quality Assessment

The accuracy of the Apple Watch’s sleep tracking goes beyond just identifying sleep stages, as it also evaluates the overall assessment of sleep quality. The device offers users several valuable metrics on sleep duration, periods of wakefulness, and heart rate variability during sleep that can indicate sleep quality. However, the device’s algorithms for interpreting this data and providing health recommendations must be more transparent, and the scientific community needs access to the underlying algorithms. This makes it difficult to evaluate the accuracy of the sleep quality assessments provided to users.

Comparative Performance with Other Devices

Sleep tracking has become a crucial feature in the realm of wearable technology. The market offers a range of devices like the Apple Watch, Fitbit, Garmin, and Withings, each employing a distinct approach to monitoring sleep patterns. In this comparison, we aim to evaluate the accuracy of sleep tracking across these devices, analyzing how they track sleep stages, overall sleep quality, and the underlying technology that enables their tracking capabilities.

Apple Watch

The Sleep app in watchOS 7 enables the Apple Watch to track sleep via motion detection using the accelerometer and heart rate monitoring. Apple’s approach to sleep tracking is simple, focusing on sleep duration rather than detailed sleep stages. It emphasizes bedtime routines and helps users achieve their sleep goals rather than providing an in-depth analysis of sleep quality or stages. While the integration with the Apple ecosystem offers a seamless experience, the accuracy of the Apple Watch for basic sleep tracking is considered acceptable. However, the Apple Watch may only be sufficient if you require detailed insights into your sleep architecture.

Apple Watch Series 9
  • CARBON NEUTRAL — An aluminum Apple Watch Series 9 paired with the latest Sport Loop is carbon...
  • WHY APPLE WATCH SERIES 9 — Your essential companion for a healthy life is now even more powerful....
  • ADVANCED HEALTH FEATURES — Take an ECG anytime. Get notifications if you have an irregular heart...
  • A POWERFUL FITNESS PARTNER — The Workout app gives you a range of ways to train plus advanced...
  • INNOVATIVE SAFETY FEATURES — Fall Detection and Crash Detection can connect you with emergency...


Fitbit is a sleep-tracking pioneer known for comprehensively analyzing sleep stages such as light, deep, REM sleep, and awake times. This is achieved using heart rate variability, movement detection, and proprietary algorithms. Fitbit’s devices provide detailed insights into sleep, including sleep scores and benchmarking against averages, making it a popular choice for users who seek an in-depth understanding of their sleep patterns. Multiple studies have confirmed the accuracy of Fitbit’s sleep tracking, demonstrating its ability to differentiate between sleep stages with high accuracy comparable to polysomnography tests.

Fitbit Sense 2
  • Learn to manage stress, sleep better and live healthier with Sense 2—our most advanced health and...
  • Manage stress and live healthier: all-day stress detection with cEDA and daily Stress Management...
  • Measure and improve sleep quality: personalized Sleep Profile(5), daily sleep stages & Sleep Score,...
  • Enhance activity: built-in GPS and workout intensity map, Daily Readiness Score(5), Active Zone...
  • Designed for all-day wear: on-wrist Bluetooth calls, texts and phone notifications(6), customizable...


Garmin’s fitness trackers and smartwatches cater to the active user, with sleep tracking as part of their health monitoring suite. Garmin devices use a combination of movement detection and heart rate variability to assess sleep stages, similar to Fitbit. They offer insights into light, deep, and REM sleep, as well as awake times, and provide users with a sleep score. Garmin’s strength lies in its integration with its overall fitness and health tracking ecosystem, offering detailed insights for fitness-inclined individuals. However, its sleep tracking is sometimes criticized for less accuracy in detecting wake times at night.

Garmin Vivoactive 5
  • Designed with a bright, colorful AMOLED display, get a more complete picture of your health, thanks...
  • Body Battery energy monitoring helps you understand when you’re charged up or need to rest, with...
  • Get a sleep score and personalized sleep coaching for how much sleep you need — and get tips on...
  • Find new ways to keep your body moving with more than 30 built-in indoor and GPS sports apps,...
  • Wheelchair mode tracks pushes — rather than steps — and includes push and handcycle activities...


Withings offers advanced sleep-tracking solutions that cater to users seeking medical-grade insights into their sleep patterns. The company’s sleep-tracking technology comprises smartwatches and a dedicated sleep-tracking mat called Withings Sleep Analyzer. The mat utilizes pneumatics (pressure sensors) and sound analysis to comprehensively analyze sleep cycles, heart rate, snoring, and sleep apnea. Withings’ approach is more clinical and has been validated by several studies for its accuracy in detecting sleep apnea and sleep stages. This makes Withings’ sleep tracking solutions ideal for those requiring accurate and detailed data to monitor their sleep quality and detect sleep disorders.

Withings ScanWatch Light
  • FSA & HSA Eligible
  • HEART RATE TRACKING - Monitor heart rate to optimize workouts, 24/7 tracking with notifications if...
  • MENSTRUAL CYCLE GUIDE - This smartwatch is great for women to log cycle phases, period duration,...
  • ADVANCED 24/7 ACTIVITY TRACKING - 40+ activities recognized with heart rate zones during workout,...
  • SLEEP TRACKER - Wake up to your Sleep Quality Score, improve your energy levels with insight into...

Other Brands

Several competitors in the market, including Xiaomi, Huawei, and Samsung, provide sleep-tracking features. They focus on measuring sleep duration, quality, and sometimes sleep stages. However, the accuracy and level of detail in their sleep analysis may vary due to the differences in their price points and target audiences.

Fitbit Sleep Score main

Limitations and Considerations

Users of the Apple Watch sleep tracker need to understand the limitations and considerations associated with this feature. Although sleep-tracking technology is advanced, it is imperfect and can be influenced by various factors. 

For instance, the accuracy of the sleep tracker can be affected by the placement of the device on the wrist, the tightness of the band, and individual differences in sleep patterns. In some cases, the device may not be able to detect specific movements, such as when a user is lying still but still awake. Additionally, the device might not fully capture the impact of sleep disturbances or conditions such as sleep apnea, as it is not designed to diagnose or treat any sleep disorders.

Therefore, it is essential to remember that the Apple Watch sleep tracker is intended to provide general information about sleep patterns and may not be a substitute for medical advice or diagnosis. It is always best to consult a healthcare professional with concerns about your sleep quality or health.

The Role of Sleep Trackers in Sleep Hygiene

Despite its limitations in accuracy, the Apple Watch sleep tracker is a valuable tool that can help promote better sleep hygiene. By tracking users’ sleep patterns, the device can raise awareness about their sleep quality and quantity, enabling them to make lifestyle adjustments that can lead to better sleep over time.

One of the ways the Apple Watch sleep tracker can encourage healthier sleep habits is by helping users maintain a consistent sleep schedule. By providing data on when they fall asleep and wake up, users can identify patterns and aim to go to bed and wake up at the same time each day. This can help regulate their body’s natural sleep-wake cycles and improve the quality of their sleep.

Another way the device can promote better sleep hygiene is by identifying factors disrupting users’ sleep. Additionally, the device can provide data on users’ heart rates, allowing them to identify any irregularities affecting their sleep.

Ultimately, the Apple Watch sleep tracker can help users become more aware of their sleep habits and make changes that can lead to better sleep quality over time. The device can positively impact users’ overall health and well-being by promoting healthier sleep habits.


When choosing a sleep tracker, users should consider their priorities: do they want simplicity and ecosystem integration (Apple), detailed sleep stage analysis (Fitbit), fitness integration (Garmin), or clinical-grade accuracy (Withings)? These devices offer varying granularity and methodology, catering to different needs. While they all provide insights into sleep patterns, their accuracy and data quality differ. 

The Apple Watch sleep tracker is a convenient tool for sleep monitoring, though its ability to detect sleep stages and assess sleep quality has limitations compared to professional sleep studies. Still, it’s a valuable device for those wanting insights into their sleep habits. Future iterations of the Apple Watch may offer enhanced accuracy and additional features that will support users in their quest for optimal sleep health as wearable technology continues to evolve.

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