Measurement of saturation without pulse oximeter on Xiaomi

Many Xiaomi smartphone owners are wondering if they can turn a gadget into a medical device. The desire to test blood oxygen levels without buying a separate device is natural, especially when a modern phone with many sensors is at hand. However, it is worthwhile to immediately mark the limits of the possible: there is no built-in hardware pulse oximeter in most Xiaomi models, alas, there is no such thing as a built-in hardware pulse oximeter.

However, the Android ecosystem and Mi Health software offer alternative solutions. Users often confuse software simulations with real-world physical measurements, which can lead to misinterpretation of health data. Understanding the way optical sensors work will help avoid fatal errors in monitoring the state of the body.

In this article, we will take a closer look at the technical capabilities of Xiaomi smartphones, existing software crutches, and real-world ways to get rough data. You will learn why a camera and flash can become a measurement tool, and the limitations of not having a specialized infrared LED.

Principal limitations of the hardware of Xiaomi

First, you need to understand the physics of the process. A real pulse oximeter uses two light sources: red and infrared. Blood absorbs light differently depending on oxygen saturation, and the difference in absorption of these two spectra gives an exact SpO2 figure. Xiaomi smartphones, even flagship ones, usually have only one flash LED, which shines white or yellowish light.

The lack of a second, infrared channel makes it physically impossible to perform classical spectrometric analysis. A phone camera can detect skin color changes caused by blood pulsations, but this is only an indirect sign. Software algorithms try to extrapolate this data using statistical models rather than direct physical measurements.

It's worth noting that some rare models or special versions of devices may have had additional sensors under the screen, but the mass segment of Xiaomi, including the popular Redmi and Poco series, does not have this option. So all applications that promise instant results use mathematical approximation, they analyze pulse rate and color reproduction, substituting values into general formulas.

⚠️ Attention: Full dependence on the readings of the smartphone in the presence of symptoms of hypoxia (dyspnea, blue lips) is categorically unacceptable.

Xiaomi engineers are implementing various proximity and light sensors, but their spectral sensitivity is not calibrated for medical purposes. Using such devices for diagnostics is always a risk of getting a false negative or false positive result.

Software Methods Through Camera and Flash

The most common way that any Xiaomi owner can use is to use a camera and flash through specialized applications, and the principle of operation is that the finger pressed against the lens changes its transparency and color in the beat of the heart, and the light passes through the fabrics, captured by the camera matrix, creating a video stream that is analyzed by the algorithm.

To implement this method, you'll need to download a third-party app from the Google Play Store, because standard MIUI software rarely contains this feature in the public domain. Popular programs like Pulse Oximeter or Instant Heart Rate use a camera to read photoplethysmography. You put your finger on the flash while you close the camera, and you wait about 30-60 seconds.

The accuracy of these measurements depends heavily on the external lighting and the density of the finger press. If you press too weakly, the light sensor will count the excess light, if you block the blood flow, and the indicators will fall. The algorithm tries to compensate for these noises, but on cheap Xiaomi models with simple cameras, the error will be higher.

There is a nuance with software image processing. Some applications on Xiaomi may conflict with aggressive camera noise cancellation, which turns on automatically in low light. This can cause the application to simply not see the pulse or give a measurement error, in which case manual camera mode or use of "video" mode with exposure fixation helps.

Integration with the Mi Health ecosystem and wearable devices

If built-in smartphone techniques fail to achieve acceptable accuracy, look to Xiaomi’s ecosystem: Mi Fitness (formerly Mi Wear) and Mi Health are central hubs for data collection. They don’t measure saturation by themselves, but perfectly synchronize data with external devices, turning the smartphone into a powerful analytics center.

The most accurate way to get data to a Xiaomi phone is to pair it with a smart bracelet or watch that supports SpO2. Models like the Mi Band 6/7/8 or Mi Watch have built-in optical sensors that work on the right principle.

The setup process is simple: you open the Mi Fitness app, go to the device section, and find the health monitoring point, and you can set the frequency of automatic measurements, and the smartphone will get this data over Bluetooth Low Energy, using minimal energy, and this allows you to monitor around the clock without having to pull out the bracelet every time.

The advantage of using a Phone + Bracelet bundle is that you can plot long-term charts. You can track how saturation changes during sleep or exercise. For Xiaomi owners, this is the most rational way, because integration works natively, without crutches and constant reconnection.

Use of IR ports and external sensors

Some of Xiaomi’s older and more specific models were equipped with an infrared port (IR Blaster), which is commonly used to control TVs and air conditioners. In theory, this port can emit infrared light, but it is not designed to receive reflected signals in the context of oximetry.

However, there is a class of external devices that connect via a charging connector (USB Type-C or Micro-USB) or an audio connector (if stored in the model), which are full-fledged pulse oximeters in miniature, and they transmit raw data to the phone, where the Mi Health app or third-party software visualizes them.

When choosing an external sensor for Xiaomi, pay attention to the protocol support OTG. Most modern Xiaomi phones support this function by default. Just insert a compatible pulse oximeter into the adapter, and the phone will determine it as an external audio device or a device. HID-gadget.

This is the only way to turn a phone into a real medical device with a high degree of reliability, which is often cheaper than an external unit, and the accuracy is higher, because they are designed solely for one task, and for people with chronic respiratory diseases, this is the optimal solution.

Analysis of third-party applications and their algorithms

There are hundreds of apps in the Play Market that promise to measure oxygen in your blood, most of them just beautiful graphs generated by a random number generator within the normal range (95-99%), but there are more advanced algorithms that try to actually analyze the video stream from the camera.

Apps like Pulse Oximeter - O2 Monitor use a camera to analyze the color change of the nail bed. The algorithm isolates the pulse wave and tries to estimate the saturation of hemoglobin. On Xiaomi phones with good cameras (the flagships of the Mi and Xiaomi series), the result can be surprisingly close to reality, with an error of 3-5%.

It's important to understand that these applications require calibration, you might be asked to enter age, weight, gender and physical activity levels, and that data is used to adjust the baseline, and without entering personal data, the mathematical model will run idle, giving the averages for the hospital.

⚠️ Note: Apps requiring access to contacts or microphones to measure oxygen are most likely spyware.

Also worth mentioning is the effect of protective glasses and films on the lens. Dirty lens or thick glass can distort color perception, which is critical for colorimetric methods. Before each measurement, wipe the camera. Xiaomi often has powerful flashes that can heat the finger, causing vasodilation and distortion of the picture of blood flow.

Factors affecting the accuracy of measurements

Even with the best available techniques, there are many variables to consider: body temperature and environment play a huge role, cold hands have spasmic peripheral vessels, making the signal weak and unreadable for the phone's optical sensors.

Having nail polish, especially dark ones, blocks light, and the way you see your fingers is not going to work, and movement is going to work, too, because even microscopic hand shaking makes noise in the video stream, which the algorithm can interpret as arrhythmia or a fall in saturation.

💡

To improve the signal, massage your finger slightly before the measurement to increase blood flow, but do not rub too hard to avoid causing redness of the skin.

The brightness of ambient light is another critical factor: direct sunlight or a bright lamp can illuminate the camera matrix, completely destroying the useful signal, and measurements are better done in a room with moderate, diffuse lighting, covering the finger and camera with the palm of the second hand or dense tissue.

Anemia also makes its own adjustments: Low hemoglobin levels change the optical properties of the blood, and algorithms that are sharpened to the norm can fail, and relying on phone measurements is especially dangerous in such cases, since the baseline has already been changed.

Frequently Asked Questions (FAQ)

💡

Xiaomi smartphone can serve as an auxiliary tool for tracking the dynamics of the condition, but does not replace professional medical equipment for serious diseases.