Xiaomi Redmi 9 smartphones feature a modern touchscreen display that responds to the slightest touch, which creates certain difficulties during phone conversations. When you bring the device to your ear, the screen must go out automatically so that your cheek does not reset the call and switch calls to hold. However, many users face a situation where the display continues to glow, blocking the interface and consuming battery power.
The main element responsible for this function is the proximity sensor located at the top of the body next to the speaker. In the Redmi 9 model, this sensor is often combined with the front camera or placed in a thin frame, which requires accurate calibration to work correctly. If the system does not receive a signal that the object is close, the screen will remain on, ignoring the position of the phone in your face.
In this article, we will discuss in detail how to force the screen to turn off during a conversation, adjust the sensitivity of the sensor and fix software failures in the MIUI shell. You will learn what hidden engineering menus are available for diagnosis and how the physical condition of the protective glass affects the operation of the entire alert system.
The principle of operation of the proximity sensor in MIUI
The technology used in Xiaomi Redmi 9 is based on infrared radiation, which is reflected from objects in front of the front panel. Infrared emits an invisible beam, and the receiver analyzes its reflection. If the distance to the object is less than 2-3 centimeters, the operating system receives a command to lock the touchscreen and turn off the backlight of the display.
In the MIUI shell, a system process is responsible for processing this data, which can conflict with third-party applications or “hang” after an update. Often users confuse the proximity sensor with the light sensor, which regulates the brightness of the screen, but the first module is responsible for quenching the screen when you call. Incorrect interpretation of the data leads to the phone “thinking” that it is lying on the table, even when you hold it to your ear.
⚠️ Warning: Using thick black-framed protective glasses or poor-quality covers can physically block the sensor’s operation area, making software setting useless.
To work properly, you need to keep the area at the top of the screen clean and free of contamination. Fat spots or dust can scatter the infrared beam, creating a false alarm or, conversely, ignoring the approach. In some cases, simple cleaning of the upper edge of the device with an alcohol napkin helps.
Basic settings of the lock screen and calls
Before you go to a complex diagnosis, you should check the standard settings of the system, which can affect the behavior of the screen. Xiaomi Redmi 9 does not have a direct button “turn off the screen when calling”, as this is the basic feature, but there are related parameters that block its work. First of all, check the settings of the theme, as third-party themes often break the standard scripts of the call interface.
Go to Settings → Lock screen and make sure features like Pocket Mode work correctly.This mode is designed to prevent accidental taps in your pocket, but it uses the same sensors as the screen damping function when you talk. If Pocket Mode is disabled or configured incorrectly, the phone may not respond to the approach to your head.
- 📱 Check if the “Always screen on” mode is enabled» (AOD), which in some versions of the firmware may conflict with sensors.
- 📞 Make sure that the Phone app does not set background activity limits or energy savings.
- 🛡️ Remove the protective glass during the inspection to exclude its effect on IR rays.
You should also pay attention to the settings of the Caller itself. Open the Phone application → Settings → Incoming calls. This may be the Approximation Sensor, which sometimes spontaneously turns off after a crash. If you have one, make sure that it is activated. In some regions and versions of MIUI, this item is hidden, and you can access it only through the engineering menu.
Engineering menu and sensor calibration
The most effective way to solve the problem is to force the sensors to calibrate through a hidden CIT (Customer Integration Test) menu, which is designed to test hardware components in the factory, but is also available to ordinary users for diagnostics. Calibration allows you to reset the reference values of the proximity sensor, forcing the system to re-remember what is "close" and what is "far".
To enter the diagnostic menu, open the Phone app and dial the combination ##6484##. If the code doesn't work, go to Settings → About Phone → MIUI version and quickly press 7-10 times on the logo until you have become a developer. Then, in the advanced settings, look for CIT or Testing.
☑️ Testing of sensors in CIT
In the test list, look for the Proximity Sensor. You will see a window with two values: current and threshold. Hold your hand to the top of the screen - the value should change (usually from 5.0 to 0.0 or vice versa, depending on the version of the sensor). If the values do not change or change randomly, press the Calibrate button.
During calibration, the system will ask you to remove your hand from the screen and then close the sensor. Follow the instructions on the screen exactly. Once the procedure is completed, the phone can reboot. It is critical that you don't interrupt the calibration process and keep the device still on a flat surface. This action reprograms the senses.--Sensor performance under current operating conditions.
Special features and gesture management
There are many accessibility features in the MIUI shell that can overlap standard system behavior. The Special Opportunities section contains settings for people with disabilities, but they also affect the touchscreen and sensors. For example, the Gesture Control or Magnification function can block the screen's response to approach.
Go to Settings → Advanced Settings → Special Features. Go through the Physical and Vision tabs. Make sure features like Touch Lock or Improver are disabled. Sometimes, activating Quick Notes (shaking the phone) causes an interrupt conflict, causing the proximity sensor to stop sending signals to the locking system.
| MIUI function | Screen impact | Recommendation |
|---|---|---|
| Pocket regime | Locks the screen in the dark when approaching | Insert for tests |
| Gesture management | Can intercept the sensor | Temporarily disable |
| One-hand mode | Changes the area of the touch | It doesn't affect the sensor. |
| Increase | Changes the scale and reaction of the Touch | Turn it off. |
It's also worth checking the "Mode in your pocket" settings. If it's on, the phone locks when the sensor is closed and the accelerometer doesn't record movement. This can interfere with normal operation during a conversation if you're holding the phone still. Try changing the sensitivity of this mode or turning it off completely for inspection.
Third-party applications and software conflicts
Often, the screen is malfunctioning because of user-installed applications for managing calls, recording conversations, or smart blockers, and applications like Truecaller, Call Recorder, or various launchers can implement their overlays (overlay interfaces) that intercept sensor control.
To identify the culprit, try to run your smartphone in Safe Mode, and to do this, press the power button, and when the off icon appears on the screen, press and hold it with your finger for a few seconds, the system will suggest that you go to Safe Mode, and if in this mode the screen goes out when you call normally, then the problem is in third-party software.
How to remove a conflicting application?
Notice applications that request permission to "Overlap Other Windows," which allows the program to draw interfaces on top of system interfaces, which often breaks the proximity sensor, check the list of such applications in the security settings, and disable suspicious ones.
Hardware problems and physical impact
If software methods don't work, consider a physical malfunction. In the Redmi 9, the proximity sensor can fail due to a fall, moisture or factory defect. Symptoms of hardware breakdown include a permanent black screen when calling (the interviewee hears but you can't see who's calling), or vice versa, the screen never goes out.
Sometimes the problem lies in the outgoing plume of the display or the sensor itself, especially if the phone has been hit or opened before. In such cases, software calibration can temporarily improve the situation, but it will not solve the problem completely.
⚠️ Note: If after the fall the screen has stopped turning off, and the calibration in CIT shows a value of "0" or "5" constantly without reaction to the hand, there is a possible physical failure of the sensor, requiring a replacement module.
As a temporary solution for hardware failure, you can use the function "Gestural Answer" or "Ear-lift" if they are available in your version of the call, but for full operation, you should contact the service center to replace the sensor or plume.
Resetting and system update
The last software method to solve the problem is to reset all settings to factory or update firmware. Errors in system configuration files can accumulate over time, especially if you often changed themes or installed beta versions of MIUI. Resetting will not delete your personal photos and contacts, but will return system parameters to the original state.
Go to Settings → Advanced Settings → Reset and Reset → Reset. Note: Choose Reset Settings instead of Erase All Data if you don’t want to lose information. Once you reboot, the phone will behave like new, and the sensors will have to be calibrated again.
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Before resetting your settings, make sure to back up important data to the Mi Cloud cloud or your computer to avoid accidental loss of information.
Also check for system updates. Xiaomi regularly releases patches that fix bugs with sensors. Go to Settings → About Phone → Update MIUI. If a new version is available, install it by pre-charging the battery by more than 50%.
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A comprehensive approach: a combination of sensor cleaning, CIT calibration and third-party app validation solves 95% of screen issues on the Xiaomi Redmi 9.