Xiaomi smart bracelets have long ceased to be just an accessory for counting steps. Modern models of the Mi Band series and Xiaomi Smart Band are equipped with dozens of sensors, advanced AI algorithms and integrated into the Mi Home ecosystem. But how exactly do these compact devices manage to track sleep to phase, measure blood oxygen levels and even warn of possible health problems? In this guide, we will analyze the hardware stuffing, software algorithms and hidden capabilities of Xiaomi bracelets, which the manufacturer does not always advertise.
If you've ever wondered why the wristband shows different data than a professional pulse monitor, or how it detects that you're asleep, here's the answers: We'll analyze each sensor, explain how Xiaomi handles raw data, and give you practical tips for customization to improve accuracy, and we'll also reveal some undocumented features that can be activated through an engineering menu or third-party apps.
Hardware platform: what sensors are hiding under the case
Xiaomi’s bracelets look minimal, but they have a whole lab hidden inside them, and even budget models like the Mi Band 6 have 6-8 sensors, and flagship versions like the Xiaomi Smart Band 8 Pro have more than 10.
- 🔴 Optical heart rate sensor (PPG) — It measures heart rate and heart rate variability (HRV) through the skin's translucent green/red LEDs. The new models use BioTracker 4 with improved accuracy.
- 🌙 accelerometer + The gyroscope tracks movement, activity (walking, running, swimming) and sleep phases, and adds a 6-axis sensor to the Mi Band 7 Pro to allow more accurate gesture recognition.
- 💡 Light sensor – automatically adjusts the brightness of the screen and helps to determine the time of falling asleep by the level of ambient light.
- 🩸 SpO2 sensor – measures blood oxygen saturation (important for assessing sleep quality and detecting apnea) Xiaomi Smart Band 8 adds 24-hour monitoring support SpO₂.
- 🔋 Thermometer – found in pro versions (e.g. Mi Band 7 Pro), tracks skin temperature for stress analysis and menstrual cycle.
- 📶 NFC-chip - in models with prefix NFC Payment is available (supports Mi Pay, Google Pay and transport cards in some regions).
All sensors work in tandem with a low-power processor (e.g., Dialog). DA14706 It's a feature of Xiaomi, which is optimized for round-the-clock operation, and it uses noise-canceling algorithms that weed out artifacts (like the shaking of the hand when measuring the pulse), which allows the bracelet to consume minimal energy without losing accuracy.
How Xiaomi bracelet tracks heart rate: technology PPG
Optical heart rate sensor (PPG, Photoplethysmography is the basis of all fitness functions of the wristband, and it works on the principle of capillary translucence: green or red LEDs illuminate the skin, and the photodiode captures reflected light. When the heart beats, blood rushes to the vessels, and the intensity of the reflected light changes - so the bracelet calculates the pulse.
Xiaomi bracelets use multipoint PPG-technology (for example, in the Mi Band 7 Pro - 4 LEDs instead of 2:
- 📊 Reduce error when driving (for example, while running).
- 🔍 More precisely to determine arrhythmia and tachycardia.
- 🌡️ Measure heart rate variability (HRV) – a key indicator of stress and fatigue.
However, PPG limiting:
⚠️ Note: The sensor can show inaccurate data at low temperature (narrowed vessels), tattoos on the wrist or a strong tan (pigment interferes with translucence).In such cases, Xiaomi recommends wearing a bracelet 2-3 fingers above the wrist.
To improve accuracy, the bracelet uses an adaptive filtering algorithm that takes into account:
- 📈 Signal amplitude (the stronger the pulse, the more reliable the data).
- 🚶 User activity (additional processing is included when walking to compensate for movement).
- 🌡️ Skin temperature (in pro-versions).
How to check the accuracy of the pulse meter?
Sleep monitoring: how the bracelet determines the phases and quality of rest
Sleep tracking is one of the most popular features of Xiaomi wristbands, which analyzes not only the duration, but also the structure of sleep, breaking it into phases:
- Waking (movement, awakening).
- Light sleep (transition phase, 50-60% of the total time).
- Deep sleep (recovery of the body, 15-20%).
- REM-Phase (rapid eye movement, dreaming, 20-25%).
To do this, the bracelet combines data with:
- 🔄 Accelerometer – captures the movements and turns of the body.
- 💓 Pulsemeter – heart rate in the deep phase decreases by 20-30%.
- 🌡️ Thermosensor (in pro-versions) - skin temperature drops by 0.5-1°C during deep sleep.
- 🌙 Light sensor – helps to determine the time of falling asleep and waking up.
Xiaomi Sleep Tracking Algorithm 3.0 (Mi Band 7/8) It uses machine learning, trained on thousands of examples of polysomnography, but there are nuances:
⚠️ Warning: A bracelet may mistakenly count lying with your eyes open as a dream if you don't move 10+ To avoid this, activate the Smart Sleep Recognition option in the Mi Fitness app settings, which takes into account the micro-movements of the eyelids.
| Sleep phase | Characteristics | How the bracelet defines it |
|---|---|---|
| Light sleep. | Superficial rest, easy to wake up | Small movements, pulse 5-10% lower than the daytime |
| Deep sleep. | Recovery of tissues is difficult to wake up | Minimal activity, pulse 20-30% lower, skin temperature drops |
| REM-phase | Dreams, brain activity as when awake | Pulse unstable, sudden movements of the arms / legs are possible |
| Awakening | Short-term or final | A sharp increase in pulse and movement |
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For more accurate sleep analysis, wear a wristband on your non-working arm (left for right-handers, right for left-handers) which reduces the number of false positives from random movements.
Activity tracking: pedometer, calories, and exercise recognition
Xiaomi bracelets automatically recognize up to 30+ activities (in Mi Band 8), including walking, running, cycling, swimming and even yoga:
- 📊 Accelerometer – analyzes the acceleration and rhythm of movements.
- 🔄 Gyroscope – determines the orientation of the hand in space (for example, machi when swimming).
- 💡 AI algorithms – compares motion patterns to Xiaomi database.
Example of work:
If the bracelet records rhythmic fluctuations with a frequency of 1-2 Hz and an amplitude of 0.5-1.5 m / s2, it recognizes walking.
- When amplitude is increased to 2-3 m / s2 and the frequency increases to 2-3 Hz - running.
If the movements are chaotic, but with periodic peaks of acceleration - strength training.
To calculate calories, the bracelet uses the formula:
Calories = (MET × Weight × Time) / 60
where MET is the metabolic equivalent (energy cost for a particular activity).⚠️ Attention: The bracelet overstates calories at short intense loads (such as a sprint or burpie) and understates with prolonged static exercises (such as a bar.
Check the step length in the profile settings
Wear a bracelet on the wrist of your working hand
Calibrate the sensor (walk 100 steps with your phone in your hand)
Update the bracelet firmware-->
SpO₂ Stress and stress: how the bracelet assesses health
Measurement of blood oxygen saturation (SpO₂) — One of the most useful but underrated features of Xiaomi bracelets, the sensor works on the same principle as the pulsemeter, but uses red and infrared LEDs, which are absorbed differently by oxygenated and deoxygenated hemoglobin.
Normal performance SpO₂:
95-100% is the optimal level.
90–94% mild hypoxia (may be the norm in the mountains)
Below 90% is a critically low level, requiring medical advice.
Xiaomi bracelet measures SpO₂ two-way:
1. Upon request -manual measurement (runs manually in the menu of the bracelet).
2. Automatically - during sleep (in models with 24-hour monitoring).
To assess stress, the bracelet analyzes:
Heart rate variability (HRV) – the lower it is, the higher the stress level.
Respiration rate (at rest, the norm is 12-20 breaths / min).
Activity (sharp movements may indicate nervousness).
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Indicators SpO₂ below 92% for 5+ If the bracelet regularly records such episodes, contact a sleepr.
Communication with the phone: Bluetooth, notifications and NFC
Xiaomi bracelets use Bluetooth Low Energy (BLE 5.0/5.2) to communicate with a smartphone:
- 📶 Low power consumption – the bracelet can last up to 14 days without recharging.
- 🔄 Two-way synchronization – data from sensors is transmitted to the phone in real time.
- 🛡️ Encryption – all data packets are protected by a 128-bit key.
The bracelet uses protocol for notifications ANCS (Apple Notification Center Service on iPhone and Mi Push Service on Android:
- 📞 Incoming calls (with the possibility of resetting).
- 💬 Messages from messengers (up to 120 characters).
- 📅 Calendar reminders.
Models with NFC (For example, Mi Band 7 NFC) support:
- 💳 Contactless payments via Mi Pay (in Russia, it works only in limited ways).
- 🚇 Transport cards (in China – Beijing Transport Card, in Moscow, Troika support is being tested).
- 🔑 Emulation of key cards for intercoms (requires settings via Mi Home).
⚠️ Note: After resetting the bracelet to factory settings NFC-The tags are erased and need to be reconfigured. Save backup through Settings → NFC → Export of data.
Software: firmware, algorithms and hidden functions
Xiaomi bracelets run on a proprietary OS (developed on the basis of FreeRTOS), which is optimized for low-power devices.
- 🔄 OS core – manages the operation of sensors and energy consumption.
- 📊 Data processing algorithms – for example, noise filtering PPG-sensor.
- 🎨 Interface and dials – Mi Band 8 supports animated themes.
Hidden functions that can be activated:
- 🔍 Engineering menu – called by pressing 5 times on the screen in the main menu (displays raw sensor data).
- 🔋 Ultra-low consumption mode – activated via Mi Fitness (Settings) → Battery → Economic regime).
- 📡 Bluetooth debugging – allows you to connect to the bracelet via nRF Connect to analyze data packets.
For advanced users:
You can install custom firmware (such as Amazfit Mod) to unlock additional features.
- Through ADB You can change the notification limits (only the last 10 are displayed by default).
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If the bracelet began to brake, reset it to factory settings through Settings → System system → Reset.It will delete all the data, but often solves the lag problems.