Apple developed a sleep staging classifier algorithm that's based on accelerometer signals derived from Apple Watch. The accelerometer signals contain information about oscillations or changes that correspond to body movements, including respiration-induced motion patterns.
Like many sleep trackers, the Apple Watch monitors sleep using a heart rate sensor and an accelerometer, which is a device that detects motion. The watch uses an algorithm developed through machine learning to analyze the information according to parameters from clinical sleep studies. It then displays the results.
The Apple Watch's sleep stage algorithm was tested in a study of 166 people who wore both an Apple Watch and polysomnography equipment. Apple Watch was about 62% accurate in detecting deep sleep, confusing it for core sleep 38% of the time. This means your Apple Watch is likely to underestimate deep sleep.
Change your sleep goal: Tap Sleep Goal, then set the amount of time you want to sleep. Change Wind Down time: Tap Wind Down, then set the amount of time you want the Sleep Focus to be active before bedtime. The Sleep Focus turns off the watch display and limits distractions before your scheduled bedtime.
If both devices are updated and you're still not seeing accurate data for your sleep, make sure you've set up a sleep schedule. Apple Watch tracks your sleep based on the sleep schedule you create. Apple Watch can also track your sleep when you manually turn on Sleep Focus.
Your hypnogram can be found below the sleep contributors under Details in the Sleep detail view. The number above the hypnogram is your "Time asleep." This is not the same as your total time in bed, which may include periods of awake time. For adults, it is recommended to get at least seven hours of sleep each night.
This time series accelerometer data serves as the input to an algorithm that classifies the signal every 30 seconds (epochs) into one of four stages: Awake, REM sleep, Deep sleep, or Core sleep.
If your watch battery dies, it won't track your sleep data. Make sure that you're wearing your Apple Watch at a comfortable fit. If your watch is too loose, the accelerometer might register too much movement during your natural sleep.
The Apple Watch offers a convenient, non-invasive solution for detecting sleep apnea, making it accessible for users who avoid traditional sleep studies. It tracks metrics to identify episodes in real-time and provide actionable insights through its integration with the Health app.
Oura Ring did not significantly underestimate or overestimate any of the four sleep stages, while Apple Watch overestimated light sleep by an average of 45 minutes and deep sleep by an average of 43 minutes.
With the normal adult averaging a total of 3-5 cycles per night, 20-25% of sleep should account for REM for every 7-8 hours spent in bed. This can be variable depending on age, lifestyle, and other factors, especially as REM intervals decline as we get older.
Oura Ring (3rd Gen)
The Oura Ring provides some of the most accurate sleep insights of any wearable and offers actionable insights to help improve sleep habits. The fact its form factor is a nice-looking ring is a major added benefit.
The phone has an accelerometer sensor built in which is very sensitive and when placed in your bed we have a record of your movements over the night. In deep sleep your muscular movements are suppressed and so in this phase the sleep graph becomes almost flat.
Apple wants you to wear your Apple Watch all the time
Before using the Apple Watch Ultra, I started wearing the Series 5 Watch at night because I wanted to use the sleep tracking features. The battery life was an issue I faced, but I usually just charged the watch during the day while I was at my desk.
How does Apple Watch do it? The gold standard to measure sleep stages in a lab is an EEG (electroencephalogram), a device worn on your head which detects brain waves. Apple Watch creates an approximation based on its accelerometer, heart rate sensor, and blood oxygen sensor.
Sleep detection being recorded when you are not actually asleep is possible if you are sedentary around your predetermined sleep window. Examples that can trigger this include: Sitting or laying down for an extended period. Reading.
To measure stress levels, smartwatches use heart rate variability. In other words, they measure the amount of time between each heartbeat. Heart rate variability is regulated by the nervous system. A more variable heart rate indicates lower stress levels whereas a less variable heart rate indicates high stress levels.
While sleep trackers can collect a lot of information about your slumber habits, they don't measure sleep directly. Instead, they often measure inactivity as a surrogate for estimating sleep. Most sleep tracking devices make some guesstimate as to how much you're actually sleeping.
In actuality, the soapy timer stops counting and disappears into a black bubble abyss if you fall short. And you probably still have dirty paws. So how does the Apple watch know when you're washing your hands? It utilizes microphones to listens for the sound of water and motion sensors to detect hand movement.
Make Sure Sleep Tracking is Turned On
Set up sleep tracking on your Apple Watch using the Sleep app on your Watch (tap “Use This Watch for Sleep”) or under Watch > Sleep on your iPhone. If you're having trouble and you've enabled the feature, you can toggle it off and on again to see if that helps.
When you wear your Apple Watch to bed, it uses the accelerometer to look for breathing disturbances while you sleep.