Approximation Sensor in Xiaomi Redmi 9T: where is it and how it works

The proximity sensor in Xiaomi Redmi 9T smartphones is a small but critical element that automatically shuts down the screen during phone calls. When you bring the device to your ear, the sensor registers the obstacle and extinguishes the backlight, preventing accidental pressing and saving battery power. However, many users face problems: the screen does not go out when you call, the sensor locks for no reason, or, conversely, the sensor ignores the approach of the hand, most often due to pollution, damage or improper calibration.

In this article, we will take a closer look at where the proximity sensor in the Redmi 9T is physically located, how it works, and what signs indicate that it is malfunctioning, and how to check the sensor’s performance using hidden menus and third-party applications, as well as what to do if it fails, and pay special attention to typical repair errors – for example, why after replacing the glass or battery, the sensor may stop working.

Physical location of the proximity sensor in the Redmi 9T

In the Xiaomi Redmi 9T, the proximity sensor is integrated into the top of the display module, next to the front camera and speaker, and specifically, it is under glass, to the left of the selfie camera, if you look at the screen in the vertical position. This is typical for most Xiaomi smartphones in the budget and mid-range segments. The sensor itself is a miniature infrared sensor that emits and picks up the reflected signal.

It's important to understand that the sensor is not visible, because it's covered by an opaque display coating, but you can tell by the characteristic small circular hole (~1 mm in diameter) in the screen bezel next to the camera, and in some models, this hole can be hidden under a black masking grid, and if you look at it from an angle, you can see it in good light.

• 📍 Exact coordinates: ~5 mm to the left of the front camera, at the level of the upper edge of the speaker.
• 🔍 How to find: Turn on the flashlight and shine on the top of the screen – the sensor will slightly reflect light.
• ⚠️ Careful: Do not confuse with the light sensor, which is located to the right (above the camera).

Inside the case, the sensor is connected to the motherboard through a flexible display plume, and when you disassemble the phone, you can see it on the back of the screen -- this is a small black chip with a transparent plastic cap, and damage to the plume or oxidation of the contacts often causes the sensor to malfunction.

Device and principle of operation of the sensor

The approach sensor in Redmi 9T works on an infrared basis, it emits a light beam that is invisible to the human eye and analyzes its reflection from objects. When you hold the phone to your ear, the beam bounces off the skin and returns back to the sensor. The chip processes the signal and tells the system to turn off the screen and block touch control.

The sensor shall include:

• 💡 IR emitter – a diode that generates infrared light.
• 👁️ IR receiver - photodiode that captures the reflected signal.
• 🧠 Microcontroller – processes data and interacts with the system.

Specifications of the sensor in Redmi 9T:

The Redmi 9T’s sensor is software calibrated, and when you first turn on your phone, the system automatically adjusts the trigger threshold, taking into account the specifics of the glass and body, and if you change the display or glass, you may need to recalibrate (see below).

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If the sensor is triggered too early (for example, when you point your hand on the screen), try calibrating it through an engineering menu.

Signs of malfunction of the proximity sensor

The proximity sensor malfunctions are different, but they all involve incorrectly turning off the screen during calls or when interacting with the phone, and here are the most common symptoms:

• 📵 The screen does not go out when you hold the phone to your ear during a conversation.
• 🔒 Sensor locks spontaneously even when you don't call.
• 🤳 The screen goes out when taking a selfie (sensor responds to hand).
• 🔄 Frequent false positives – the screen is turned on and off for no reason.
• 🚫 No response to approaching hand in test applications.

The causes of these problems can be divided into two categories:

1. Software failures – firmware errors, incorrect settings, conflicts with applications (for example, after the MIUI update).
2. Hardware malfunctions - contamination of the sensor, damage to the plume, cracks on the glass, oxidation of contacts.

The most common fault is pollution of the infrared window sensor — dust, greasy prints or glue residues after changing the glass block the IR signal, and problems can occur after the fall of the phone, especially if the impact occurred on the top of the screen.

⚠️ Attention: If the sensor stopped working after the display was replaced, it is likely that the master did not move the protective gasket or damaged the plume.

How to check the proximity sensor on the Redmi 9T

Before you bring your phone to the service, you can diagnose the sensor yourself using built-in tools and third-party applications.

Method 1: Testing through the Engineering Menu

1. Open the Phone application and enter the code:

##6484##

(Some firmware may run ##4636##, then select Hardware testing.)

2. In the menu that opens, select Proximity Sensor.

3. Cover the sensor with your hand, the value should change from 5 (no obstacle) to 0 (obstacle detected). If the numbers do not change, the sensor is defective.

Method 2: Checking through the application

Install one of the sensor testing apps from Google Play, for example:

• CPU-Z (Sensors tab).
• Sensor Test (from Innovative Apps)
• Phone Doctor Plus.

Run a proximity sensor test and check the response to the approach of the hand. Normally, the graph should drop sharply to zero when the sensor is closed.

Method 3: Visual examination

Take a magnifying glass and look carefully at the top of the screen next to the front camera.

• 🕳️ Pollution or scratches on the glass above the sensor.
• 💧 Traces of moisture or corrosion (if the phone fell into the water).
• 🔌 Damage to the plume (visible only when disassembled).

If the sensor is externally clean, but does not work, the problem is more software.

Calibration of the proximity sensor

If the sensor is triggered too early or doesn't respond to the approach, it can be recalibrated. In Redmi 9T, this is done through an engineering menu or special commands.

Method 1: Through the Engineering Menu

Enter the code:

##6484##

(or #4636### → Hardware testing)

2. Select Proximity Sensor.

3. Press Calibrate and follow the instructions on the screen. You usually need to close and open the sensor with your hand.

Method 2: ADB (for advanced users)

If the engineering menu is not available, you can use ADB:

1. Connect your phone to your PC and enable USB Debugging in the developer settings.

2. Enter the command:

adb shell am start -a android.settings.PROXIMITY_CALIBRATION

This will open a hidden calibration menu.

After calibration, restart the phone and check the sensor.

⚠️ Attention: Poor calibration can make the sensor worse. If problems worsen after the procedure, reset the sensor settings to factory via the same menu.

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Calibration only helps with software failures, and if the sensor is physically damaged, the display module or the plume needs to be replaced.

What to do if the sensor is not working

If the diagnosis showed that the sensor is defective, act on the algorithm:

1. Clean the sensor. Wipe the top of the screen with an alcohol napkin (no pressing!) Sometimes it's enough to remove the greasy prints.
2. Check the firmware. Update MIUI to the latest version or reflash your phone if the crash occurred after the update.
3. Reset the settings. Reset the factory settings (save the data!) This will help if the software is the problem.
4. If the sensor does not respond to calibration and cleaning, you need to replace the display module or plume.

The cost of repair in official Xiaomi services:

Self-repair is possible if you have experience disassembling smartphones. Redmi 9T will require:

• 🔧 Set of screwdrivers (cross, flat, suction cup for the screen).
• 🧴 Thermopaste for plumes (if reconnection is required).
• 📱 New display module or plume (order from a trusted site, such as AliExpress with a seller rating above 98%).

Frequent Repair Mistakes and How to Avoid Them

Many users try to fix the proximity sensor with their own hands, but make mistakes that only exacerbate the problem.

• 🛠️ Using sharp objects to clean the sensor – this scratches the glass and damages the IR window.
• 💦 Water the sensor with liquids (alcohol, water) - moisture can get inside and cause corrosion.
• 🔥 Heating the screen with a hairdryer in an attempt to “dry” the sensor – this will damage the glue and plumes.
• 🔄 Install non-original parts without compatibility checks (e.g. Redmi display) 9A won't fit).

If you decide to replace the display module, pay attention to:

• 📋 The model of the module must be exactly the same as the original (for example, the model of the module, T100036-01 for Redmi 9T).
• 🔌 The sleeves – make sure they are intact and without slacks.
• 🛡️ Protective pad – it must be moved from the old screen or replaced with a new one.

After replacing the display, be sure to recalibrate the sensor, even if it seems to work, and this will prevent false positives in the future.

FAQ: Frequent questions about the proximity sensor in the Redmi 9T