Mi Band Sleep Tracking: How Does It Work?

The Mi Band is a popular sleep-tracking device that can help you understand your sleeping habits and patterns. The Mi Band series uses a combination of biosensors, including an accelerator, gyroscope, and PPG sensor, to detect body movements, heart rate, breathing patterns, and other factors such as temperature, noise, and light. This data is then analysed to provide insights into your sleep quality, duration, and stages (light, deep, and REM). While the Mi Band is not the most in-depth sleep-tracking solution available, it offers surprisingly useful features at an affordable price, allowing users to improve their sleep habits and overall health.

Tracking sleep quality

The Mi Band series from Xiaomi offers sleep tracking features that can help you understand your sleeping habits and patterns. The Mi Band uses three biosensors to detect your sleep: an accelerator, a gyroscope, and a PPG sensor. These sensors work together to analyse your sleeping pattern by tracking your heart rate, breathing pattern, and other factors like temperature, noise, and light.

The accelerator is a six-axis accelerometer that detects slight motions and gravity changes, converting wrist movements into sleep patterns. It identifies zero body movements as a state of sleep and rigorous movements as a state of awakening. The gyroscope, on the other hand, is a motion sensor that detects angular displacement like tilting and rotation.

The PPG sensor detects your heart rate by shining infrared light on the portion of the skin illuminated with light to detect the blood flow rate. This helps the Mi Band understand your sleep parameters, including light sleep, deep sleep, and Rapid Eye Movement (REM) sleep. Light sleep is a transitional stage between being awake and asleep, where you can be easily woken up and body movements are minimal. Deep sleep is important for building immunity and recovering from physical fatigue. REM sleep is when you dream and is crucial for restoring mental health.

While the Mi Band can provide insights into your sleep quality, it may not be the most accurate or in-depth sleep-tracking solution available. Some users have reported that the Mi Band 8, for example, struggles to recognize different stages of sleep accurately. If you're specifically interested in sleep tracking, other devices like Fitbit and Apple Watches might provide more precise measurements.

Sleep regularity

The Mi Band's sleep tracking feature offers insights into your sleep regularity. This feature displays your previous night's sleep in the context of the previous week's sleep trend, allowing you to identify patterns and make informed decisions about your sleep habits. The Mi Band can track your sleep duration, the specific times you fell asleep and woke up, and differentiate between sleep stages: deep sleep, light sleep, and REM sleep. It also provides a sleep score, a quantifiable measure of your overall sleep quality, derived from factors such as sleep stage duration and total sleep time.

The Mi Band's sleep tracking capabilities are enhanced by its ability to detect and analyse various factors that contribute to understanding your sleep patterns. It uses biosensors, including an accelerator, gyroscope, and PPG sensor, to detect body movements and distinguish between states of sleep and wakefulness. The accelerator, or accelerometer, is a six-axis sensor that detects slight body motions and gravity changes during sleep. The gyroscope, on the other hand, is a motion sensor that detects angular displacement, such as tilting and rotation. These sensors work together to identify periods of sleep and wakefulness based on your body's movements.

Additionally, the PPG sensor plays a crucial role in detecting your heart rate. It does this by shining infrared light onto your skin and measuring the blood flow rate in the illuminated area. This information helps the Mi Band understand your heart rate patterns during sleep. The Mi Band also considers other factors, such as breathing patterns, temperature, noise, and light, to provide a comprehensive analysis of your sleep environment and its potential impact on your sleep quality.

While the Mi Band's sleep tracking accuracy has been questioned, particularly in comparison to competitors like Fitbit and Apple Watches, it still provides a valuable entry point for understanding your sleep habits. The data gathered by the Mi Band can be a starting point for improving your night routine and sleep hygiene. By analysing your sleep regularity and patterns over time, you can identify areas where you may need improvement and make adjustments to your sleep habits and environment to promote better sleep quality.

Sleep cycle stages

Sleep is a body process that allows the body to rest, repair, and restore itself. It is not uniform, and over the course of the night, a person will typically go through four to six sleep cycles, each composed of four individual stages. The sleep stages are determined based on an analysis of brain activity during sleep, which shows distinct patterns that characterise each stage. The first sleep cycle is often the shortest, ranging from 70 to 100 minutes, while later cycles tend to be longer, ranging from 90 to 120 minutes.

The two phases of sleep are rapid eye movement (REM) and non-rapid eye movement (NREM) sleep. REM sleep is the stage of sleep where most dreams occur, and it makes up about 25% of total sleep time. During REM sleep, brain activity resembles that of a waking brain, and the eyes move behind closed eyelids. The first REM cycle is typically the shortest, at around 10 minutes, with each subsequent cycle increasing in length, up to an hour.

NREM sleep is composed of three different stages, ranging from N1 to N3. Stage 1, or N1, is when a person first falls asleep, and this stage usually lasts from one to seven minutes. It is easy to wake someone up during this stage, but if they are not disturbed, they can quickly move into stage 2, or N2. During N2, the body enters a more subdued state, with a drop in temperature, relaxed muscles, slowed breathing and heart rate, and a new pattern of brain waves. Brain activity slows, but there are short bursts of activity that help resist being woken up by external stimuli. Stage 2 sleep can last for 10 to 25 minutes during the first sleep cycle, and each N2 stage can become longer as the night goes on. The higher the stage of NREM sleep, the harder it is to wake someone up.

The Mi Band line of devices can track sleep cycles and help users understand their sleeping habits. It does this by tracking the heart rate, breathing pattern, and other factors like temperature, noise, and light to analyse sleep patterns. The Mi Band has three biosensors: an accelerator, a gyroscope, and PPG. The accelerator detects irregular motions, and the gyroscope is a motion sensor that detects angular displacement like tilting and rotation. The PPG sensor shines infrared light to detect the blood flow rate in the portion of the skin illuminated with light. Mi Band models with blood oxygen sensors can also monitor breathing quality.

Sleep tracking accuracy

The accuracy of sleep tracking on the Mi Band varies according to different user experiences. The Mi Band 8, the latest in the series, has been described as having "not so good sleep tracking accuracy". It cannot recognize different stages of sleep, and other trackers like the Fitbit and Apple watches are considered better for measuring sleep.

The Mi Band uses a PPG sensor to detect heart rate and a built-in accelerometer to detect motion and a gyroscope to detect angular displacement like tilting and rotation. It also uses a heart rate sensor to estimate when the user falls asleep. Once the user is asleep, Mi Band models with blood oxygen sensors monitor breathing quality. The Mi Band is considered reasonably accurate in detecting when the user falls asleep and wakes up, but it has been known to be inaccurate in recording sleep activity when the user wakes up in the middle of the night. It has also been observed that the Mi Band is inaccurate in recording sleep data when the user gets up early in the morning but remains in bed.

The Mi Band's sleep tracking feature is not a medical device to track sleep and is instead a rough estimate. It cannot be reliably used to compare data from one person to another. The accuracy of the sleep tracking feature depends on several factors, some of which may not be under the user's control.

The Mi Band provides a sleep score on a scale of 0-100 to quantify overall sleep quality. This score is derived from sleep stage duration, total sleep, and other factors. The higher the score, the better the sleep quality. The Mi Band also provides a sleep quality analysis that explains whether the user got enough sleep or if their sleep quality was worse than usual. It also displays the previous night's sleep in comparison to the last week's trend.

Heart rate and motion detection

The Mi Band series from Xiaomi uses a combination of heart rate and motion detection to track sleep. The device uses a PPG sensor to detect heart rate by shining infrared light onto the skin and measuring blood flow rate. It also uses an accelerometer to detect motion and a gyroscope to detect angular displacement like tilting and rotation. These sensors work together to identify when the wearer has fallen asleep and to track their sleep patterns.

The accelerometer in the Mi Band detects slight motions and gravity changes, converting these wrist movements into sleep patterns. It identifies zero body movements as a state of sleep and more rigorous movements as a state of awakening from sleep. The gyroscope, meanwhile, detects angular displacement, providing additional data on the wearer's sleep movements.

The Mi Band also offers sleep quality analysis, providing insights into the duration and quality of sleep, including deep sleep, light sleep, and REM sleep. It can also monitor breathing quality through blood oxygen sensors, tracking the wearer's breathing patterns throughout the night.

While the Mi Band's sleep tracking features are useful, they may not be as accurate as those of other devices like Fitbit or Apple watches. The Mi Band 8, for example, has been noted to have less accurate sleep tracking capabilities and may not recognize different stages of sleep as effectively as other devices.

Frequently asked questions