Users of the popular Xiaomi Redmi Note 9 Pro often face a situation where the screen during a conversation does not go out or, conversely, does not light up after the phone is removed from the ear. This is a classic symptom of a sensor failure, which is responsible for determining the distance to the object. Understanding where exactly this element is physically located is the key to solving the problem, whether it is a wrong sticker of the protective glass or a software glitch of the system.
In this article, we will take a look at the design features of your smartphone so you can visually identify the location of the sensor, and we will also conduct a deep diagnostic of the software part, because in 90% of cases the problem is not a breakdown, but a contamination or software conflict, and accurate knowledge of the design will help you avoid unnecessary trips to the service center.
It's worth noting that Xiaomi engineers in this model (used) a rather specific layout of the front panel, which often causes confusion among owners. Many are looking for a separate hole that simply does not exist, or seal an important area with a thick protective glass. Let's understand how the proximity sensor in your device works.
Design features of the front panel of the Redmi Note 9 Pro
The Redmi Note 9 Pro has an IPS LCD screen with a cutout in the top left for the front camera. This is where the main sensors are hidden. Unlike the old, wide-frame models, all sensors are hidden under the display layer or located in close proximity to the camera lens. A virtual sensor is exactly the case when there is no physical window, but the software system reads the data.
The main module we're interested in is an infrared emitter and a receiver, and they work in pairs: one emits an invisible beam, and the other reads its reflection. If the beam reflects instantly, the phone knows what is being held to the ear, and the screen is extinguished. Xiaomi often uses technology integrated directly into the body under the screen, making it invisible to the eye.
But there's a second type of sensor that uses software algorithms and accelerometer data, but this model focuses on a physical IR sensor, and the sensitivity zone is at the top of the display, and if you use a black-framed security glass that covers this area, it's going to be disrupted, and that's the most common cause of user complaints.
Technical details of the IR sensor
Exact location of the sensor: photo description
To find the sensor, you don't have to disassemble the phone. Look at the top of the screen next to the speaker. In the Redmi Note 9 Pro, the proximity sensor is located in a narrow strip above the display or directly below the top edge of the screen, often combined with the light sensor. Visually, this can look like a small darkened window or be completely hidden under the glass of the matrix.
If you swipe down the top, you can feel a little groove, or just a little bit darker, and that's where you don't have to get greasy finger marks or dust, and the cleanliness of that area is critical to the proper operation, and sometimes the covers make the sides too high, which also blocks the sensor.
For clarity, let’s look at the comparison with other models so you understand the difference in Xiaomi’s approaches:
| Smartphone model | Location of the sensor | Sensor type | Sensitivity to pollution |
|---|---|---|---|
| Redmi Note 9 Pro | Top frame / under the screen | Infrared | Tall. |
| Redmi Note 8 Pro | Top frame (separate window) | Infrared | Medium |
| Xiaomi Mi 10 | Under the screen (virtual) | Ultrasonic/Optical | Low. |
| Poco X3 NFC | Top frame | Infrared | Tall. |
As you can see from the table, the Redmi Note 9 Pro uses a classic but clean circuit. If you've recently changed your display or glued glass, make sure that the wizard doesn't hit the area with glue. Mechanical locking is the first thing to rule out.
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The sensor is at the top of the front panel, often hidden under the black screen frame, and any overlap in this area (glass, cover, dirt) leads to failures.
Software Diagnostics through Engineering Menu
Before you put your phone in repair, you need to make sure that the hardware is in good shape. There's a built-in tool in the MIUI shell to check all the sensors. It's the most reliable way to tell if your phone can see your ear. Use a special code to run the diagnostics.
Open the Phone application (number dial) and enter the following character combination:
##6484##Once you enter the last digit, the CIT (Customer Interface Test) menu will open. You don't need superuser rights. In the test list, look for a item called "Proximity Sensor" or "Proximity Sensor." It's usually at the top of the list or in the Common section.
- 📱 Click on the "Proximity Sensor" to enter the test mode.
- 🖐️ Hold your palm tightly to the top of the screen (where the sensor is located).
- 👀 Put your hand away and look at the value on the screen.
- ✅ If the value changes from "5.0" (or Near) to "0.0" (or Far), the sensor is in good working order.
If the values don't change or freeze on one metric, it indicates a problem. This can be both a software driver failure and a physical damage to the plume. Calibration often helps correct incorrect readings if the sensor is physically intact.
Calibration of the proximity sensor
If the test values float or the sensor is not working properly (the screen goes out on its own), calibration is required. At Xiaomi, this process is automated, but requires certain actions to be performed. Reset calibration returns the factory sensitivity settings of the sensor.
In the same engineering menu (CIT), in the sensor check section, there's usually a "Calibrate" or "Calibrate" button. Press it and follow the instructions on the screen. Typically, the system will ask you to remove your hand from the phone and then close the sensor. Don't move your phone at this point.
⚠️ Warning: Do not calibrate if you have a thick black-framed protective glass on the screen, and this will knock the settings, and the sensor will think that the hand is always held up.
Once you've calibrated successfully, the phone can restart. Check normal by making a test call. If the problem persists, try the next method, reset via the app. Some versions of MIUI have a separate "Mi Test" or "Service" app where you can select "Approximation Sensor" and click "Calibration."
☑️ Calibration algorithm
Influence of protective glasses and accessories
One of the most common causes of failure is the incompatibility of accessories. The market is crowded with protective glasses for the Redmi Note 9 Pro, but not all of them take into account the location of the sensors, especially for full-glue glass black.
If the black glass frame covers the area of the sensor (even partially), the infrared beam cannot escape or reflects off the inner layer of glass, creating the illusion that the phone is near the ear, which causes the screen to go out immediately after the start of the call and does not turn on until you put the phone down.
- 🛑 Check if the glass covers the area above the speaker.
- 🧼 Clean the top of the screen of fat and dirt with an alcohol napkin.
- 🔍 Remove the cover and check the work without it.
- 💡 Try temporarily removing the protective glass for diagnosis.
Sometimes it helps to stick glass with a cutout under the sensor or use thinner films. Mechanical obstruction is the number one enemy for optical sensors. If you see that the glass has a hole in the area of the sensor, but there is a problem, then the hole is offset or the sensor is deeper.
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Use transparent protective glass without a black frame to eliminate the possibility of overlapping the sensor. Transparent glue allows IR rays better than a tinted layer.
Solving software conflicts and resetting settings
If the hardware is good and the glass is transparent, the problem may be in the software. Application conflicts, especially those that control calls or screens (such as Black Screen or various launchers), can block the sensor. Try booting into Safe Mode.
To do this, press the off button, and when the menu appears on the screen, keep your finger on the "Stop" (or "Stop") for a long time until the prompt to go to Safe Mode appears. If in this mode the sensor works perfectly, then the third-party application is to blame.
⚠️ Warning: Before resetting your settings to factory settings, be sure to back up your data in the Mi Cloud cloud or on your computer, as all information will be deleted.
A radical but effective method is a full reset (Wipe Data) that deletes all temporary files and resets system configs that may have been damaged after the MIUI update. Go to Settings → About Phone → Settings Reset → Erase all data. After that, the phone will be like new.