Xiaomi smartphone owners often face a situation where the screen does not go out during a conversation and the cheek is accidentally pressed by the reset or volume button. This is a classic symptom of the incorrect operation of the sensor, which is responsible for the device’s response to the approach of objects. Understanding where the proximity sensor on the Xiaomi Redmi 9 Pro is physically located is key to solving 90% of the problems with the screen panel during calls.
Unlike budget models, where the sensor can be placed on the front panel in the form of a noticeable eye, Redmi 9 Pro engineers have applied hidden placement technology. This makes the device more aesthetic, but complicates diagnosis and maintenance. If you are planning to replace the glass or faced with a software failure, you need to know the exact topology of the front panel of your gadget.
Our guide will go into detail about the design features of this model, explain how the infrared emitter and receiver work, and offer proven calibration methods. We won’t use complex technical terms without explanations so that even a beginner can understand the nuances of their smartphone.
Design features of the sensor in the Redmi 9 Pro
Many users mistakenly search for a visible element on the screen surface, believing that the sensor should be visible to the eye. However, the Redmi 9 Pro uses In-display Proximity Sensor technology. This means that the physical module is located directly below the display, at the top, closer to the speaker. On top it is closed with a layer of protective glass and a screen matrix, making it completely invisible when turned off.
The principle of operation is based on emitting an invisible infrared beam and analyzing the reflected signal. When you hold the phone to your ear, the beam reflects off the surface of the cheek and returns to the receiver. The system detects the change in the intensity of the reflection and tells the MIUI operating system to turn off the touchscreen and backlight. If the sensor is contaminated or displaced during disassembly, this process is disrupted.
⚠️ Attention: an attempt to find a sensor on the outer surface of the case and seal it "for verification" will not give results, since in this model it is hidden under the display.
It is important to understand that the absence of a visible hole does not mean the absence of a sensor; on the contrary, such a design requires more precise calibration by software, since the thickness of the protective glass and the presence of a protective film can make adjustments to the operation of the sensor, which is why after replacing the display or glass, it is often necessary to force reconfiguration through the engineering menu.
Exact location of the module under the display
If you are planning to repair or replace a display module yourself, you need to know the exact location of the component. The proximity sensor in the Xiaomi Redmi 9 Pro is integrated into the main display plume or is on a separate board at the top of the case, but most often it is soldered on the matrix itself or is located in the upper speaker zone. In most cases, it is a tiny black square measuring no more than 2-3 millimeters.
When disassembling the device, it's important not to damage this microscopic element, which is very fragile and sensitive to mechanical stress. If you use a suction cup or a mediator to open the body, avoid pressure in the upper central part of the screen where the infrared sensor is located, and damage to this element will make it impossible to make calls in normal mode.
You can use a flashlight to visually detect the sensor when you're disassembling the phone. Turn on the flashlight on the other phone and light up the top of the Redmi 9 Pro's screen at an angle. You can notice a light glow or a dark spot under the matrix, which is the module you want. When you're in the operating state, when you call, it can light up slightly in red or purple when you look through the camera of another smartphone with an IR filter.
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When replacing the display, be sure to wipe the inside of the new glass with alcohol in the sensor area to remove the factory protective film that blocks IR rays.
Software calibration through the engineering menu
Often the problem is not the physical location, but the software settings fail. The Android operating system in the MIUI shell allows for deep calibration of sensors. There's a special engineering code that allows you to access the hardware testing, which is the first step you need to take before you go to the service center.
To get into the test menu, open the standard Phone app and dial the combination ##6484##. Once you enter the last digit, the CIT (Customer Information Test) menu will automatically open. In the test list, look for the "Proximity Sensor" or "Approximation Sensor" item. When you click on it, you will see the current sensor readings.
The calibration process is as follows:
- 📱 Place your phone on a flat surface so nothing covers the top of the screen.
- 👆 Press the “Calibrate” button on the screen.
- 🙌 Close the top of the screen with your palm, simulating the ear, and wait for the readings to change.
- ✅ Remove your hand and make sure the value is back to its original state (usually 5.0 or 0.0).
If you press the Start or Calibrate button, the test is successful (green lights on), the hardware is good. If the test doesn't work, try to wipe the screen and repeat the procedure. In some cases, several calibration cycles are required to stabilize the readings.
☑️ Checking of operability
Influence of accessories and protective glasses
One of the most common reasons for sensor malfunction is poor-quality protective glass or film. Because the sensor in Redmi 9 Pro is hidden under the display, any thickening over it can block infrared radiation. Cheap security glasses often have a black border or opaque layer of glue at the top that physically blocks the path of the beam.
High-sided covers can also cause problems, and if the side of the case enters the upper speaker area, it can create a permanent illusion of approach, in which case the phone will think that it is in the ear all the time, and the screen will go out immediately after turning on or not respond at all to touch during the call.20
To diagnose this problem:
- 🔍 Remove the protective glass and check the sensor without it.
- 📱 Remove the cover and make sure that the sides do not cover the upper end.
- 🧼 Clean the top of the screen of fat and dirt that can scatter the IR rays.
If the problem has disappeared after removing the protection, you need to replace the accessory with a better one that is compatible with your model.
Why are cheap windows blocking the sensor?
Comparison with other Xiaomi models
Understanding the differences in design helps you better navigate the smartphone lineup. While the Redmi 9 Pro uses a hidden sensor, in older or budget models (such as the Redmi Note 8 or Redmi 9C), the sensor is often placed in a separate hole next to the speaker, which makes it easier to replace, but degrades the appearance of the device.
Flagship models like the Mi 11 or Xiaomi 13 use even more sophisticated systems, including laser rangefinders or ultrasonic sensors that work even through thick glass. However, the mid-range segment, which our hero belongs to, uses a classic IR sensor that requires a line of sight (through the screen) to work.
Below is a table comparing sensor types in popular models:
| Smartphone model | Type of sensor | Location. | Difficulty replacing |
|---|---|---|---|
| Redmi 9 Pro | Hidden (In-display) | Under the display | Tall. |
| Redmi Note 8 | Open (Visible) | Over the screen | Low. |
| Xiaomi Mi 11 | Ultrasonic/Laser | Under the display | Very high. |
| POCO X3 NFC | Hidden | Under the display | Tall. |
As you can see from the table, the Redmi 9 Pro is in the same group as modern smartphones, where aesthetics are put above ease of repair.
Diagnostics of hardware faults
If the software calibration doesn't work and the security windows are removed, it could be a physical failure. The proximity sensor could fail due to a fall, moisture, or just factory failure. In the Redmi 9 Pro, it can be soldered onto the display plume, which means that the entire display module needs to be replaced when it breaks.
Symptoms of hardware failure include:
- 📉 Complete lack of response to closing the top of the screen with the palm of your hand during a call.
- 🔥 Strong heating of the top of the phone in the area of the speaker.
- 💧 The liquid enters the speaker (water can close the contacts of the sensor).
For an accurate diagnosis in the CIT engineering menu, look at the values. If you close your hand with the numbers that don't change at all (remain at 0.0 or 5.0), chances are the sensor is dead. If the values jump randomly even without touching, maybe short circuit or oxidation of the contacts.
⚠️ Warning: If the phone has recently fallen, the sensor may have moved away from the plume.Opening the case and pressing the connector tightly can solve the problem without replacing parts.
Solving Program Conflicts
Sometimes the sensor is functional, but it's blocked by third-party applications. Various "memory cleaners," call blockers, or conversation recording apps can intercept the sensor's control. MIUI also has a Pocket Mode feature that uses the proximity sensor to lock the screen in your pocket. A failure in this algorithm can lead to false positives.
Try turning off Pocket Mode in your call settings. Go to the Phone app, click three dots in the corner, select Settings, and find the appropriate item. If the problem disappeared after disabling this feature, then the conflict was in the software logic of the system.
It's also worth checking for system updates. Xiaomi regularly releases patches that fix sensor bugs. Go to Settings → About Phone → MIUI version and check for updates. Sometimes resetting all settings to factory helps, but this is an extreme measure that requires data backup.
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In 80% of cases, the problem is solved by removing the protective glass or recalibrating through the engineering menu, without the need to replace parts.