Location and configuration of the proximity sensor in Xiaomi Redmi 9

Budget smartphone owners often experience unexpected screen behavior during a conversation when the display lights up or, conversely, goes off without a user command. In the Redmi 9, this process is controlled by a special module that is physically hidden under the protective glass, which creates the illusion of its absence. Understanding the principle of operation of this component is necessary for the correct diagnosis of problems, since many users mistakenly believe that the sensor is completely missing or defective due to design features.

Modern manufacturing technologies have enabled manufacturers to integrate sensitive elements directly into the display structure, eliminating the need for cutouts or individual holes in the top frame. Redmi 9 uses a so-called virtual sensor that works in conjunction with the accelerometer and MIUI software algorithms. This solution reduces the cost of production, but requires finer adjustment and calibration to work stably in real-world conditions.

If you notice that the phone doesn't turn off the screen when you reach the ear, or if it blocks dialing when you first touch it, it may be a software failure rather than a physical injury. Knowing the location of the active zone and testing correctly will help you avoid a visit to the service center. Below, we'll take a detailed look at how the system works and what steps you need to take to make it work properly.

Physical location and working principle

Unlike older smartphone models, where the proximity sensor was a separate window next to the speaker, the Xiaomi Redmi 9 integrated it into the display matrix itself. The physically active element is at the top of the screen, usually in the center or with a shift to the conversational speaker. Visually, it is impossible to see when the screen is turned off, since it is hidden behind a layer of glass and LCD-panel.

It's based on infrared light and reflection analysis. When you hold the phone to your head, the infrared beam bounces off the skin surface and returns to a sensor that sends a signal to the system to block the touchscreen. It's critical to understand that any protective films or glass with an opaque bezel at the top can block this invisible beam, causing malfunctions.

The sensor works closely with software that filters false positives. MIUI algorithms analyze data not only from the IR sensor, but also from the gyroscope to understand the position of the device in space. If the phone is lying on the table with a screen up, the system ignores the "approach" signals, preventing accidental locking.

⚠️ Warning: Using thick, black-edged protective glass that doesn’t match factory markings is the most common cause of a broken sensor in the Redmi 9.

To check for the physical presence of a reaction, you can use the engineering menu, which will be discussed below, but before proceeding to complex tests, make sure that the top of the screen is clean and not closed by foreign objects.

Diagnostics through CIT Engineering Menu

The most reliable way to check the health of the sensor hardware is to use the built-in diagnostic CIT mode. This tool allows you to test all components of the smartphone in isolation from the main operating system, which eliminates the influence of third-party applications. You do not need root rights or a computer connection to enter the diagnostic mode.

The process of running the test is simple and takes no more than a minute, you need to open the standard Phone application and type a special combination of characters, and after entering the last sign, the menu will open automatically.

##6484##

Once you open the test list, look for the Proximity sensor (usually at the top of the list or a corresponding number, such as 3 or 4). Click on it to go into check mode. The screen will show a numerical value and instructions to put the phone on a flat surface or close the top of the screen with your hand.

In the test mode, you'll see how the numbers change: when the hand is removed, the value should be 5.0 (or close to the maximum), and when you close the top of the screen with your palm, the value should drop to 0.0. If the numbers change smoothly and without delay, then the sensor is physically healthy.

• 📱 5.0 - Open sensor, no obstacles.
• 🖐️ 0.0 - Sensor closed, object detected.
• ⚠️ Permanent 0.0 - possible sticking or breakage.
• 🔋 Constant 5.0 – the sensor does not see obstacles (calibration problem).

If the sensor is working correctly in this menu, but there are problems in life, then the reason is software calibration or application conflict, and if there is no reaction at all, you may need to replace the display module or the plume.

Sensor calibration procedure

Even a properly designed sensor can malfunction if it is calibrated down, often after a firmware update, screen replacement, or simply over time. Xiaomi smartphones have a hidden reset and reset sensitivity feature that helps return the device to factory settings.

To do the calibration, you'll need the engineering menu again. Log in to ##6484## and select the Proximity sensor test. At the bottom of the test screen, you'll see the Calibration button. You click on it and you start the automatic setup process.

When calibrating, the screen may flash or go out. Don't interrupt the process or touch the top of the phone. The system will determine the minimum and maximum light values and write them down in the controller's memory. Once completed, a success or error message will appear.

If the automatic calibration didn't work, you can try manually resetting data through the developer menu, but it requires more care. CIT-The menu is enough to restore normal operation.

⚠️ Note: Do not calibrate in bright sunlight or under a directional lamp, as external illumination may distort the results of the setting.

After successful calibration, be sure to restart your smartphone so that the changes take effect. Check the sensor's performance in normal call mode by holding the phone to your face.

Software settings and limitations of MIUI

The MIUI shell has many features that can conflict with the approach sensor, in particular, various energy saving modes or “smart” functions can limit the sensor’s background activity to save battery power, and it is also worth checking the call settings in a standard application.

Open the Phone app, click on the three dots in the top right corner, and select Settings. Find the Incoming Calls or Additionals section. This may have a proximity sensor switch that is sometimes disabled by default or knocked down after an update.

Another important setting is In-Pack mode, which uses the same sensor but with different sensitivity thresholds. If it doesn't work properly, it can affect normal calls, and try turning it off temporarily to see if the problem goes away.

• 📞 Call settings – check for sensor activation.
• 🛡️ Pocket mode – may conflict with the main mode.
• 🔋 Energy savings – limit the operation of background sensors.

Also worth mentioning are third-party calling apps like Truecaller or Google Phone, which may have their own screen management settings that override MIUI system settings. If you use a third-party call, check its internal settings.

Effects of accessories and physical damage

As mentioned earlier, security glass is the main enemy of virtual sensors. If you recently pasted a new glass with a wide black bezel that covers the top of the display, the problem is almost certainly it. Infrared light can't penetrate the opaque layer, and the phone "thinks" it's permanently closed.

In addition, contamination, greasy spots or cracks at the top of the screen can scatter the IR ray, leading to false positives. Even a thin layer of dust in the speaker located next to the sensor area can make it worse. Regular cleaning of the top of the smartphone with soft cloth can solve the problem.

Physical damage, such as bumps or falls, can cause the plume to detach or shift components under the screen.In Redmi 9, where the sensor is integrated into the display, a hit to the top can damage the sensitive element even if the glass is intact.

If you carry your phone in a tight case with high sides, make sure it doesn't press on the top edge of the screen.Constant mechanical pressure can distort the sensor readings.

Comparison with other models and problem table

To better understand the situation, it is useful to compare the sensor behavior in the Redmi 9 with other popular models. The table below shows the main differences and typical problems that are typical for different devices in the line.

As you can see from the table, Redmi 9 is a group of devices with integrated sensors, which makes them more vulnerable to accessory quality, but more protected from dust entering the case. Understanding this difference helps to quickly find the root of the problem.

Owners of devices with a separate module (like the Note 8) are easier to diagnose a breakdown visually, whereas in the case of Redmi 9 requires software verification, which is an important nuance when buying parts or accessories.

Radical Solutions and Resetting

If neither calibration nor removal of the protective glass helped, there is a software reset option, sometimes errors accumulate in the system that interfere with the correct processing of signals from the sensor, resetting the settings to the factory (Factory Reset) can eliminate the software conflict.

Before performing a full reset, be sure to back up all important data, as this process will remove all files from the internal drive. Go to Settings → About Phone → Settings Reset → Clear everything.

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Before a full reset, try simply clearing the cache of the Phone and Google System Services app, often without deleting personal data.

In extreme cases, if the problem persists even after flashing the device, it is a hardware malfunction. In the Redmi 9, this most often means replacing the entire display module assembly, since the sensor in this model does not usually change separately.

⚠️ Warning: Self-disassembly of the Redmi 9 smartphone to replace the plumes can damage the fragile screen and loss of warranty.If you are not confident in their abilities, contact the service.

Remember, software techniques help 90% of the time if the sensor is physically intact. Don't rush to change the hardware until you've tried all the options for customizing the software.

Frequently Asked Questions (FAQ)

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In most cases, the problem is solved by removing the inappropriate protective glass or recalibrating through the engineering menu.