Garmin's Sleep Tracking: How Does It Work?

Sleep tracking devices such as the Garmin watch use an accelerometer, heart rate, and heart rate variability to estimate sleep stages and provide a sleep score. This allows the device to determine the time you fall asleep and wake up, as well as the quality of sleep. The watch measures your heart rate and motion to estimate your sleep stages, tracking several metrics to help you monitor and improve your sleep. It is important to note that no device is 100% accurate, and there might be inconsistencies in the results.

Accuracy of sleep tracking

Sleep tracking devices such as Garmin watches measure your heart rate and motion to estimate your sleep stages. The accuracy of sleep tracking in Garmin watches has been a topic of discussion, with some users questioning how the device differentiates between sleep and pre-sleep relaxation.

Garmin watches with Advanced Sleep Monitoring use heart rate, heart rate variability, and an accelerometer to understand when the wearer is sleeping. This method allows the device to determine sleep stages and the time the wearer wakes up. While this technology has improved since 2018, it is important to note that no device can provide 100% accuracy in sleep tracking.

Research suggests that Garmin watches are about 78% accurate in measuring sleep versus awake time and only about 38% accurate in measuring how long it takes the wearer to fall asleep. The accuracy of detecting and measuring sleep stages (deep sleep, light sleep, and REM sleep) is possibly even lower, with research indicating inconsistent results.

It is worth noting that the accuracy of sleep tracking in Garmin watches can be improved by ensuring proper placement on the wrist. The watch should be worn snugly, just below the wrist bone. Additionally, users should disable Battery Saver mode during sleep and enable sleep mode if they want daytime naps to be included in their sleep statistics.

While Garmin's sleep tracking technology provides valuable insights into sleep patterns, it is not perfect. Users should interpret the data with a degree of flexibility, understanding that it is meant to provide estimates rather than exact measurements of their sleep.

Sleep stages

Sleep is a complex and dynamic process, typically consisting of several distinct stages that an individual cycles through multiple times during a night of sleep. The Garmin sleep tracking system identifies and monitors these different sleep stages to provide users with detailed insights into their sleep quality and patterns.

Garmin's Advanced Sleep Monitoring technology employs a combination of heart rate tracking, heart rate variability measurements, and an accelerometer to accurately determine an individual's sleep stage at any given moment. Heart rate tracking involves measuring the user's heartbeats per minute, while heart rate variability refers to the time interval between each heartbeat. The accelerometer, on the other hand, detects and measures physical movement. By analysing these data points, Garmin devices can distinguish between different sleep stages and provide a comprehensive understanding of sleep quality.

Garmin categorises sleep into four primary stages: awake spells, REM (Rapid Eye Movement) sleep, light sleep, and deep sleep. Awake spells refer to periods when an individual is not asleep, which can include lying down with eyes closed or simply being still and relaxed. REM sleep is characterised by rapid eye movements and is associated with dreaming. It is considered a crucial stage for memory consolidation and cognitive function. Light sleep occurs between waking and deeper sleep, and it is during this stage that an individual can be easily awakened. Deep sleep, as the name suggests, is the stage of sleep where an individual is in a state of profound slumber, difficult to awaken from. This stage is essential for physical recovery and the release of vital hormones that regulate bodily functions.

While Garmin's sleep tracking technology offers valuable insights into sleep patterns, it is important to recognise that no device can achieve 100% accuracy in sleep stage measurement. Research suggests that the accuracy of detecting and measuring sleep stages may be lower than that of simply distinguishing between sleep and awake states. Nevertheless, Garmin's sleep tracking provides a good overall picture of an individual's sleep habits, allowing users to make informed decisions to improve their sleep quality.

Sleep spells

Garmin's Advanced Sleep Monitoring is available on most of the company's smartwatches and fitness trackers with optical heart rate monitors. This feature requires both heart rate and heart rate variability, or the period between each heartbeat, to function. Additionally, it utilizes the device's accelerometer to understand when you are sleeping. This method allows Garmin devices to not only determine your sleep stage but also the time you wake up.

The accelerometer plays a crucial role in tracking sleep, especially on older or more simplistic Garmin watches that may not have optical heart rate monitors. While the data from these devices is less granular, it still provides valuable insights into sleep patterns.

To ensure accurate sleep tracking, it is important to wear your Garmin watch snugly but not too tight on your wrist, just below the wrist bone. It is worth noting that Garmin does not include daytime naps in your sleep statistics unless the watch is placed in sleep mode. However, these naps will contribute to improving your Body Battery figure.

Daytime naps

Garmin's sleep tracking has been criticised for not recording daytime naps. While the device can track one sleep cycle per day, it is harder for it to catch a nap as the user's metrics have to match a sleep stage for a certain amount of time. When setting up a Garmin device, users are asked to set a sleep window, and the in-depth sleep tracking will only kick in during those hours. This means that if a user takes a nap outside of the sleep window, the nap will not be recorded.

While it is not possible to manually add a nap as a separate sleep session in the Garmin Connect app, it is possible to include a nap by manually changing the sleep window for that day to start when the user went to sleep for their nap, and then changing the wake-up time to when they woke up from their nap. This will result in a large awake block in the middle of the sleep window, but the app will add up the time spent asleep during the different stages. However, this method of recording naps may result in an inaccurate sleep score, as the long awake period in the middle of the sleep window may drag the score down, even if the nap was beneficial.

Blood oxygen saturation

The Pulse Ox feature on compatible Garmin smartwatches provides insights into a user's blood oxygen saturation levels. This is done by measuring the amount of light absorbed when light is shone into the skin, which indicates how much oxygen is in the bloodstream compared to its maximum capacity. This figure is delivered as a percentage, with higher percentages being more favourable.

Garmin's method of pulse oximetry examines the smaller vessels in the skin, known as peripheral oxygen saturation (SpO2). Readings are taken from the wrist, and while they are designed to provide an estimation, they can offer valuable insights. The Pulse Ox feature can be enabled during sleep to monitor blood oxygen saturation levels, which is particularly useful for those with conditions such as sleep apnea.

Sleep apnea is a condition where breathing stops and starts during sleep, and it is often associated with low blood oxygen saturation levels. Some users have reported that their Garmin watches showed oxygen levels dropping to the mid-80s or high 70s during sleep, which is considered abnormal. Normal blood oxygen saturation levels are typically considered to be between 90% and 100%, although some sources suggest that levels below 92% are abnormal.

It is important to note that Garmin smartwatches are not designed to be used as diagnostic tools, and users should be cautious about battery drain when using the Pulse Ox feature. Additionally, factors such as sleeping position and arm placement can also affect blood oxygen readings. For more accurate measurements, users can compare their Garmin readings with those from a medically certified SpO2 device.

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