Xiaomi Redmi 9A is a popular budget device, but its design has its own features that often confuse users when searching for sensors. The main question that worries owners is where exactly the proximity sensor is hidden, since it is almost impossible to see it visually on the front panel, this is due to the fact that the company’s engineers decided to integrate the sensor directly into the display module, hiding it under a protective glass at the top of the screen.
The absence of a visible hole or darkened area above the display is the result of a desire to maximize the ratio of screen area to the body. Unlike older models, where the sensor could be carried out in a separate window, it uses hidden installation technology. Understanding this design feature is critical for those who are planning repairs or trying to understand why the screen does not go out during a conversation.
In this article, we will discuss in detail the physical location of the sensor, methods of its software verification and how to fix common malfunctions, you will learn how to distinguish a software failure from a physical failure and what actions can help return the device to work correctly.
Physical location of the sensor under the screen
On the Redmi 9A, the proximity sensor is located in the upper center of the front panel, directly above the visible region of the matrix, it is under the protective glass layer and does not have a separate physical hole, which requires high accuracy during assembly, since any displacement of the plume or module itself can lead to incorrect operation of the locking function of the screen.
Structurally, the sensor is an infrared emitter and a receiver that work in pairs. The infrared beam is emitted through a microhole or a translucent piece of glass that is not visible to the naked eye. When you bring the phone to your ear during a bell, the beam bounces off the surface and returns to the receiver, signaling the system to extinguish the display.
It is important to understand that this model lacks a physical light sensor in the classical sense (a separate window), since its functions are often combined or implemented programmatically through the algorithms for analyzing images from the front camera in newer models, but the 9A uses a classic, albeit hidden, hardware bundle. The location at the top is due to the logic of use: this zone is applied to the user’s head.
⚠️ Warning: Attempts to drill a hole or mechanically impact the top of the glass in search of a sensor will lead to irreversible damage to the matrix and loss of warranty.
Knowing exactly where you're going to put it helps in diagnostics, and if you notice that the top of the screen responds differently to touch, or has a subtle change in hue under certain light, it might be related to the sensor's operating area, but 99 percent of the time, that area is visually indistinguishable from the rest of the display.
How to check the operation of the proximity sensor
Before you take the device into the service or disassemble it, you need to make sure that the software and the sensor itself are working properly. The MIUI shell, which is installed on the Redmi 9A, has a built-in engineering menu for testing all components, accessed through the standard Phone application.
To run the diagnosis, dial ##6484##. This action will automatically open the CIT menu. This is a complete list of all the modules on your smartphone. You need to find a item that might be called the Proximity Sensor or the Approximation Sensor, which is usually at the top or middle of the list.
- 📱 Click on the “Proximity Sensor” menu item to go into Test Mode.
- 🖐️ Hold your hand to the top of the screen for a distance. 2-3 see without touching the glass.
- 👀 Watch for the change in values: the distance should change from 5.0 (far) to 0.0 (close).
- ✅ If the values change correctly, the hardware is good, and the problem lies in the settings or software.
Some firmware versions may have different paths. Alternatively, go to Settings → About Phone → Kernel Version and quickly press 5-7 times on Kernel Version. The same testing menu will open. If the sensor is unstable in this menu (values jump without touch or don't change), this indicates a physical problem or a critical driver failure.
⚠️ Note: Do not use protective glass with a black opaque stripe at the top during the test, they can block the operation of the infrared sensor.
If the test is successful, but when real calls are made, the screen still lights up in your pocket, the problem may be calibration. The system gets the right signal, but the trigger thresholds are set incorrectly, and this is a common situation after a display is replaced or settings are reset.
Sensor calibration procedure
Calibration is a sensor sensitivity adjustment process that allows the system to correctly interpret the distance to the object. On the Xiaomi Redmi 9A, this procedure can be done independently through the engineering menu we discussed earlier. This often solves the problem of phantom presses or unlighted screen.
Enter the CIT menu using ##6484## and select "Proximity Sensor." In the window that opens, you'll see the Calibration button. Click on it and follow the instructions on the screen. Usually, the system will ask you to remove your hand from the screen and then close the sensor.
☑️ Checklist of correct calibration
It takes no more than 30 seconds. If the calibration is successful, you will see a green lettering or a message "Pass", and then you need to restart the device to take effect, and in some cases you need to repeat the procedure 2-3 times to achieve a stable result.
There is also a software way to reset calibration via hidden Android settings, but it is less reliable on MIUI. To do this, you need to dial ##7780## in the Phone app, which will reset the application settings and calibrations, but will not delete personal data (photos, contacts).
It is important to calibrate in good light, but not in direct sunlight, which can "light up" the sensor. Also make sure that the top of the screen is clean from grease and dirt, which can distort the readings.
Influence of protective glasses and accessories
One of the most common reasons for the sensor to malfunction on the Redmi 9A is the wrong accessories, and because the sensor is hidden under the glass, any additional coating at the top of the screen affects the passage of infrared radiation.
Cheap security windows often have a black perimeter bezel, and if that bezel comes into the sensor area (even a millimeter), it blocks the signal, and the phone thinks it's in the ear all the time, and the screen goes out as soon as the call starts, preventing the user from pressing the speaker or keyboard.
- 🛑 Black glass frame covers the sensor zone, blocking the IR beam.
- 💎 Thick tempered glass reduces sensitivity, requiring you to bring the phone close.
- 🧩 Incomplete fit of glass creates an air cushion that distorts the reflection of the signal.
The solution to this problem is to neatly remove a piece of the black bezels above the sensor with a blade or needle, if you're confident in your abilities. However, the safer option is to replace the accessory with a model with a cutout for the sensor or a fully transparent film. Transparent films tend not to interfere, because the material misses the infrared spectrum.
⚠️ Note: When removing the black frame from the glass, be extremely careful not to scratch the display of the smartphone and not damage the oleophobic coating.
Some bookcases have a magnetic fastener or a tight cover that, when closed, can mechanically press on the sensor area, causing false positives even in the pocket.
Program conflicts and MIUI settings
Sometimes the problem is not hardware, but software conflicts. The MIUI shell has many features that can interfere with basic sensors. In particular, Pocket Mode is designed to prevent accidental taps, but when it crashes, it can lock the screen for no reason.
Check the settings of this feature. Go to Settings → Lock screen → Pocket mode. Try turning off this option and check if the sensor behavior changes. If the problem disappears after the shutdown, then the sensor is working fine, but the protection algorithms were too aggressive.