Modern wearables have evolved from simple pedometers to sophisticated medical gadgets that can monitor cardiovascular health in real time. Xiaomi Watch S1 is equipped with a new generation optical sensor that provides high accuracy measurements even during intensive training. Understanding the principles of the sensor allows users to get the most reliable data about their health.
The process of taking readings seems elementary, but many owners face errors or inability to start measuring. Optical sensor requires tight fit to the skin and no foreign interference to work properly. In this article, we will discuss all the nuances of operation, from basic settings to calibration in difficult conditions.
The proper performance of the monitoring system depends not only on the hardware, but also on the software algorithms that process the data flow. Biometrics can be distorted due to tattoos, hair on the wrist or improper positioning of the strap.
Principle of operation of optical pulse sensor
The monitoring system is based on PPG (Photoplethysmography) technology, which uses light waves to determine the volume of blood in the capillaries. Xiaomi Watch S1 emits green light, which is absorbed by hemoglobin, and analyzes the reflected signal. The faster the heart beats, the more often there are changes in the intensity of reflected light, which is recorded by the sensor.
The accuracy of the measurements depends on the quality of the contact between the back of the watch and the skin. If the device dangles or air enters between the body and wrist, the light scatters, and the algorithms cannot build the correct pulse wave, which is why a tight fit is critical.
⚠️ Warning: Having thick wrist hair or dark tattoos in the sensor area can significantly reduce the accuracy of measurements or make them impossible, as the pigment and hair cover block the passage of light.
To minimize errors, the system uses multiple LEDs and photodetectors that work in a bundle, which allows you to filter the noise that occurs when you move your hand, but when you jerk or vibrate, the optical sensor can temporarily lose signal, which is reflected in the graphics in the form of dips.
Why is the green light on?
Basic instructions: how to start measuring manually
To get the data right at a given time, you need to initiate a forced measurement, which puts the sensors in the maximum polling frequency mode, ignoring the energy-saving algorithms of background work, and manual measurement is especially useful before or immediately after training.
The startup process is simple and doesn't require a deep dive into the menu. You need to unlock the watch screen and find the appropriate app. The interface of the Xiaomi Watch S1 is intuitive, and the system's response to commands is instant.
☑️ Procedure for measurement
During the measurement process, try to keep your hand relaxed by putting it on a table or lowering it along the body. Any tension in the muscles of the forearm can squeeze the vessels and distort the heart rate reading. Wait for the final value to appear on the screen.
Set up automatic monitoring in the application
Permanent heart monitoring is possible only with the right scanning frequency settings, managed through the mobile application Mi Fitness (formerly Zepp Life), which syncs with the clock over Bluetooth, and flexible settings allow you to find a balance between data accuracy and device autonomy.
You'll find the health section in the profile menu, and you'll find the frequency option, so you can choose a fixed interval, like every 10 or 30 minutes, or leave the smart mode, where the watch decides when to check your heart rate.
- 📱 Minute monitoring: provides a detailed picture, but quickly drains the battery.
- ⚡ Smart mode: measures the pulse less often at rest and more often with activity.
- 🔋 Manual mode: saves charge, measurements only on the user's command.
Change settings are applied automatically after synchronization. If you plan a long trekking or marathon, it is recommended to temporarily increase the frequency of measurements so as not to miss the dangerous zones of the pulse zones.
💡
For maximum autonomy on the trips set the measurement interval of 30 minutes – this is enough to track the overall dynamics, but the battery will live much longer.
Use during training and sports
Sports modes on the Xiaomi Watch S1 activate a special sensor algorithm that increases the frequency of the sensor survey to several times per second, which is necessary to build an accurate schedule of changes in heart rate in dynamics and correctly calculate calories consumed. Without the inclusion of sports mode, the data can be less detailed.
When running, cycling or cross-flight, it's important to consider sweating. When you get under the body, sweat drops can create a lens effect or, conversely, scatter light, which leads to surges in readings. A tight strap in this case is a necessity, not just a recommendation.
If you are a sportsman with active brushwork (tennis, boxing, golf), the error of the optical sensor can increase due to constant shock loads on the wrist, in such cases, the optical method is sometimes inferior to the chest pulsemeters, transmitting data via ANT+ or Bluetooth.
| Activity | Recommended treatment | Expected accuracy | Features |
|---|---|---|---|
| Running (cardio) | Running outside | Tall. | Stable rhythm of movements |
| Cycling | Cycling | Medium | The vibration of the steering wheel can make noise |
| Powerful. | Free exercise | Low. | The wrist often shrinks, blood flow changes |
| Swimming | pool | Tall. | Water improves contact, but water resistance is needed |
After you finish your workout, the data is automatically stored in the history, and the analysis of your heart rate recovery after exercise is a great indicator of your fitness: the faster your heart rate returns to normal, the better your heart is trained.
Data interpretation and pulse zones
The numbers only make sense in the context of your individual settings. The Xiaomi Watch S1 calculates the pulse zones based on the age you specified when setting up your profile. Understanding these zones helps you train more efficiently and safely.
There are five major intensity zones. The first is warm-up and recovery, where the heart is still working; the second is ideal for burning fat and developing endurance; the third is aerobic, where the heart muscle develops; the fourth and fifth are anaerobic, work at the limit.
⚠️ Attention: Long stay in the fifth pulse zone (90-100% from maximum) without special training can be dangerous to health and lead to overtraining.
You can see a color graph on the app showing how much time you've spent in each zone, and you can adjust your workout schedule by zone, so if you're trying to lose weight and you're in the red zone all the time, you should lower your intensity.
💡
Training in the second and third pulse zones is most effective for burning fat and developing basic endurance without risk to health.
Resolving problems with pulse measurement
Sometimes users are faced with a situation where the watch shows a dash or clearly incorrect values (for example, 200 beats at rest).The first step should always be to check the purity of the sensor.
The second common reason is that you can easily put your finger under the strap, you can't get enough contact, especially in winter, when the cold makes the vessels narrow and the signal weaker, so you should fasten the strap tighter or move the watch up your forearm.
- 🧼 Clean: Wipe the sensor with a soft cloth without pile.
- 🔁 Reboot: Restart the clock to reset software errors.
- 📲 Update: Check for firmware in the Mi Fitness app.
If software methods don't work, there may be hardware failure or sensor damage. In rare cases, a full reset to factory clock settings helps, but this is an extreme measure. Calibration of the sensor as a separate feature on the menu is usually not required, the system does it automatically.
What do I do if my pulse jumps?
Comparison with medical devices
It is important to understand the difference between consumer electronics and medical equipment. Xiaomi Watch S1 is certified as a fitness tracker, not a medical device. its readings can have an error of 3-5 beats per minute compared to an electrocardiograph or a professional pulse oximeter.
Optical sensors are inferior to electrical sensors (thoracic) exactly when the rhythm changes dramatically. For example, during interval training, the pulse increases abruptly, and it takes the clock 5-10 seconds to catch up with the real value.
However, for trend tracking, rest and overall activity, the accuracy of a smartwatch is more than enough: it captures the night pulse, which is an important marker of recovery, and the key is not to use the watch to make diagnoses.