Modern smartphones, including the popular Xiaomi Redmi Note 9, feature a variety of sensors that make the device more comfortable to use. One key element is the proximity sensor, whose task is to automatically extinguish the screen during a phone conversation when you bring the phone to your ear. This prevents accidental cheekstrokes and saves battery power. However, users often face a situation where the screen continues to burn or, conversely, goes out too early, interfering with normal communication.
The problem with the Redmi Note 9’s locking display can be caused by software failures in the MIUI shell, as well as physical obstacles closing the sensor. Device owners need to understand how this mechanism works to correctly diagnose a malfunction, and in most cases, the solution lies in the correct calibration or the correct location of the protective glass.
In this article, we will take a look at all aspects of sensor configuration, look at hidden engineering menus and suggest effective methods of solving the problem, learn how to distinguish a software bug from a hardware breakdown and can return the phone to normal functionality without going to the service center.
The principle of operation of the proximity sensor in MIUI
The proximity sensor in Xiaomi smartphones is an infrared sensor located at the top of the display, usually next to the speaker. When you start a conversation, the system sends a signal to the emitter, which is reflected from the object (your ear) and returns to the receiver. Based on the time of return of the signal, the processor decides to lock the screen.
In the MIUI shell, this process is handled by a separate system service that can conflict with other applications, such as a messenger or navigator running in the background sometimes intercepts the sensor's control, and it's important to understand that the sensor works in conjunction with the accelerometer, determining the position of the phone in space.
⚠️ Warning: If you use a thick protective glass with a wide black frame, it can block the sensor’s work area, causing false positives or a complete failure of function.
Stable operation requires that the area around the top end be clean. Fat spots, dust, or moisture can distort infrared radiation, making the phone "think" it's near the ear, even when it's on the table. Regularly rubbing this area with soft cloth is a simple but effective way to prevent it.
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Use microfiber to wipe the top of the screen before important calls to eliminate the impact of contamination on the sensor.
Basic calibration through the engineering menu
The most reliable way to fix a screen lock malfunction is to calibrate through a special engineering menu, a built-in diagnostic tool available on all Xiaomi devices, which does not require a superuser’s (Root) license to log in, making the method safe for the average user.
The calibration process takes only a couple of minutes, you have to open the Phone app and enter a special code, and once you enter the last digit, the menu will open automatically. Find the hardware testing section, often referred to as the Single-item Test or simply the Proximity Sensor.
- 📱 Enter the code ##6484## in the dialer to enter the engineering menu. CIT.
- 🔍 Find the Proximity Sensor item in the list and click on it.
- 👐 Close the top of the screen with your hand and remove it, watching the change in values (0/1 or Near/Far).
- 💾 Press the Calibration or Pass button after successful verification.
If the values don't change when you close the sensor with your hand, it may be hardware-related, and then software calibration won't help, and you'll need a deeper intervention or replacement of the component, but in 90% of cases on the Redmi Note 9, this procedure restores the correct logic of the operation.
☑️ Sensor calibration
Settings in the hidden menu Proximity
There is an alternative way to customize that is available through the standard settings menu, but hidden from the eyes of the average user, which is especially useful if the engineering menu does not open or does not work correctly, and you can reset the accumulated calibration data to factory values.
To access these settings, go to Settings, then select About Phone. Find the "kernel version" or "MIUI version" line and quickly tap it 7-10 times. This action activates a hidden menu known as Proximity Sensor Calibration.
In the window that opens, you'll see the current distance value. If it's different from zero, when nothing is closing the top of the screen, press the Calibrate button. The phone will ask you to remove your hand from the screen, and then, on the contrary, close the sensor, and after the procedure is completed, the device will reboot, and the settings will apply.
| Parameter | Normal value. | Failure value |
|---|---|---|
| Distance (Distance) | 5.0 cm | 0.0 cm or >10 cm |
| Status (Status) | Far (far away) | Near (Close) |
| Raw Data (Raw Data) | Dynamic. | A frozen number |
| Calibration Result | Success | Fail |
Note that after resetting the calibration, it may take several reboots to fully stabilize the system.
What to do if calibration fails?
Influence of protective glasses and covers
One of the most common reasons why the screen on the Redmi Note 9 doesn't go out is because of accessories. Security glass manufacturers often don't take into account the exact location of the sensors in specific models. The black glass frame can partially or completely overlap the infrared port.
Also, a poor-quality glue or air gap between the screen and the glass creates a prism effect, dissipating the signal. If you notice a problem immediately after you stick a new glass, the reason is almost certainly it. In such cases, only replacing the accessory with a model labeled as "approximation sensor compatible" helps.
High-sided cases can also create shadows over the sensor, especially for thick shock-proof cases, and when talking, the phone in the case may not feel the cheek approaching because the cover itself creates a permanent obstacle.
- 🛡️ Check if the black glass frame enters the speaker area.
- 💧 Make sure there are no air bubbles in the sensor area under the glass.
- 🧼 Wipe the screen with an alcohol napkin to remove the greasy plaque.
- 📱 Remove the case and check the sensor without it.
⚠️ Warning: Some types of tempered glass have low quality oleophobic coatings that quickly wear off and start to shine, interfering with the work of optical sensors.
If glass replacement is not possible, there are software crutches, like the Approach Sensor-Reset app, that force the sensor to be calibrated to accommodate the new coating, but it's a temporary solution, and the best result is the use of quality accessories.
Program conflicts and system updates
Sometimes the problem is not hardware, but software. Android operating system in conjunction with MIUI can receive updates that change the algorithms of the sensors. Bugs in a particular version of the Redmi Note 9 firmware can lead to ignoring the sensor signals.
Check for system updates in the Settings menu → About Phone → MIUI version. Often developers release patches that fix exactly such errors. If you have a beta version of the firmware installed, it is recommended to roll back to a stable branch, since there is less likelihood of encountering critical bugs.
It's also worth checking the list of installed applications. Third-party calls, voice recorders or conversation recording apps can intercept the sensor's control. Try to start the phone in Safe Mode. If this mode goes out correctly, then one of the apps you installed is to blame.
To enter Safe Mode, press the off button, and when the menu appears on the screen, press and hold the "Stop" option until the prompt appears to go to Safe Mode, which will allow you to diagnose the software conflict without deleting data.
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If the sensor is working perfectly in safe mode, then the problem is in a third-party application, not in the system or hardware.
Radical methods and resetting settings
If none of the above methods worked, the last software option is a complete reset, which will return the phone to the “out of the box” state by deleting all user data, so be sure to back up important information.
Reset eliminates deep errors in system configuration files that may have been damaged as a result of an incorrect update or failure of the file system. To perform, go to Settings → Advanced Settings → Recovery and Reset, and select Reset.
Once the phone is reset, you can reboot it. Don't install all the apps at once. First, check the calls and the sensor on the clean system. If the problem is gone, you can gradually return the apps, and see if the crash happens again.
In rare cases, when even a complete reset does not help, it can be a physical failure of the sensor plume or a contact breaks out inside the housing, in which case only qualified repairs in the service center with a replacement module will help.