It primarily uses the gyroscope or accelerometer to track your movements and also detect which stage of the sleep cycle you are in. Some smartwatches use heart rate sensors to monitor your heart rate reading. Your heart rate lowers while sleeping also varies when you reach the different stages in the sleep cycle.
Accelerometers. Most sleep trackers measure sleep quantity and quality by using accelerometers, small motion detectors. Accelerometers measure how much movement you're making while you sleep. This data is then analyzed using an algorithm to estimate sleep time and quality.
Most new wearables also track the sleep stages you cycle through throughout the night. But “in terms of tracking light, deep, and REM sleep, basically all of the devices performed at only a medium level of accuracy,” says Chinoy. Translation: There's only about a 50-percent chance your data is accurate.
So far, research has found that compared to polysomnography tests – which experts use to diagnose sleep disorders – sleep trackers are only accurate 78% of the time when identifying sleep versus wakefulness. This accuracy drops to around 38% when estimating how long it took participants to fall asleep.
The Apple Watch shows more light or core sleep and less deep sleep than the Fitbit. Tracking your sleep stages and cycles is most accurately done by polysomnography; it's not as simple as monitoring your heart rate all night.
Adults need an average of 84-108 minutes of deep sleep each night. This makes up roughly 25% of total sleeping time in adults, though the percentage increases for babies and decreases for people over 65 years old. Failure to get adequate deep sleep can result in short and long-term health problems.
For healthy adults, spending 20-25% of your time asleep in the REM stage is a good goal. If you get 7-8 hours of sleep, around 90 minutes of that should be REM.
Can an Apple Watch Detect Sleep Apnea? Like Fitbit and other wearables, the Apple Watch can detect certain parameters like heart rate and blood oxygen saturation that may indicate sleep apnea, but it cannot comprehensively detect or diagnose sleep apnea.
This stage is deep sleep. During this stage, your brain produces delta waves, very slow brain waves. It's hard for someone to wake you up during this stage. You have no eye movement or muscle activity.
These four sleep stages are called non-rapid eye movement (non-REM) sleep, and its most prominent feature is the slow-wave (stage IV) sleep. It is most difficult to awaken people from slow-wave sleep; hence it is considered to be the deepest stage of sleep.
In terms of sleep tracking, however, the device is not nearly as advanced as other wearable trackers I've tested firsthand. If you don't mind a simpler sleep app with a customizable alarm, sleep mode, and basic data tracking, then the Apple Watch might be a great fit — especially if you are physically active.
Note: 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. To receive sleep data from Apple Watch, it must track your sleep for at least four hours each night.
According to a press release from Apple, “Using signals from the accelerometer and heart rate sensor, Apple Watch can detect when users are in REM, Core, or Deep sleep.” Currently, your Apple Watch can kind of guess how much you've slept if you turn on “Sleep Focus,” based on how much you move around while you sleep.
Researchers concluded the Fitbit was equivalent to the actigraph in almost every way. Yet, when compared with polysomnography, the Fitbit was largely underestimating deep and REM sleep, missing roughly half of the former and a third of the latter. It also overestimated light sleep.
While all types of sleep appear to be essential, deep wave sleep could be considered the most essential. If your sleep is restless and non-restorative, you may lack sufficient deep sleep. REM sleep assists memory differently than deep sleep, focusing on social-emotional memories and even salvaging forgotten memories.
Some people with insomnia experience changes in their sleep cycles and, as a result, may have more stage 1 sleep and less deep sleep. Stress and aging can also reduce levels of deep sleep. Additionally, people with conditions such as schizophrenia and Alzheimer's disease experience less slow wave sleep.
Hypersomnia is usually indicated by long sleep periods and excessive sleepiness or excessively deep sleep. It may be associated with difficulty in awakening – the person may feel confused or disoriented (sleep drunkenness).
Yes, you can dream in all sleep stages, but dreams that are vivid and emotional mostly happen during REM sleep. You are also more likely to experience lucid dreams during REM sleep.
You'll feel more rested and refreshed when you wake up from light sleep. In contrast, you'll be sluggish and groggy if you start your day from deep sleep. Although reaching deep sleep is essential for rest, you also must finish the deep sleep and the next stage before you wake up to reap the benefits of light sleep.
Taking a melatonin supplement can help increase deep sleep in a few ways. First, it can help to regulate your sleep cycle. This makes it easier for your body to fall into a deep sleep state. Second, melatonin can help to reduce stress and anxiety.
Adults generally average 1-2 hours of deep sleep per night, somewhere between 15 and 25% of your nightly sleep. Most of our deep sleep comes in the first sleep cycle of the night, usually 45-90 minutes. Age has a major effect on how much deep sleep we get each night and how much we need.