The problem of spontaneously turning on the screen during a conversation or, conversely, its cancellation when the interlocutor has not finished a phrase is familiar to many smartphone owners. On Xiaomi devices, including the popular model of the Redmi Note 9, a special sensor is responsible for this, which often requires manual activation or calibration. Without the correct operation of this module, comfortable communication becomes impossible, since the user’s cheek constantly presses random buttons on the display.
Unlike some other manufacturers that integrate this feature at the kernel level without the possibility of turning off, the MIUI shell provides a separate software switch. Its absence from the default menu often confuses users, causing them to think about hardware malfunction. However, in most cases, it is enough just to activate a hidden option or conduct a simple setup procedure through the engineering menu.
This guide will not only help you find the switch you need, but also help you understand the way the infrared sensor works on the top of the case, and will help you understand the standard activation methods, deep calibration methods, and software conflicts that can block the sensor from working, and following these steps will allow you to return the phone to its normal functionality without going to the service center.
⚠️ Warning: Before you start any manipulation of system settings or engineering menus, make sure that the protective glass or film does not overlap the top of the screen where the sensor is located.
The operating principle and location of the sensor on the Redmi Note 9
Understanding the physical basis of the device helps to diagnose the problem more quickly. The Redmi Note 9 uses a classic infrared sensor consisting of an emitter and a receiver. When you bring the phone to your ear, the emitter emits invisible light that reflects off the surface of the cheek and is picked up by the receiver. The system receives a signal about the proximity of the object and programmatically turns off the touchscreen and display.
The location of this element on Xiaomi is often controversial. Unlike older models with a speaker removed, the Redmi Note 9 sensor is integrated directly into the area of the speaker. It is hidden under the grid or black stripe at the top of the screen, which is why any contamination, greasy spots or improperly pasted protective glass with a black bezel can completely block its operation.
Technical details of the IR sensor
It's important to note that the software's signal processing algorithm is constantly analyzing the sensor data, so if you hold the phone on your outstretched hand, the sensor should not respond, but if there are software errors, the sensitivity threshold can be shifted, and the phone will respond even to the hand holding the device or to clothes in your pocket.
Activation through the standard settings menu
The easiest and safest way to turn on the proximity sensor on the Xiaomi Redmi Note 9 is to use the built-in MIUI shell interface. The developers have provided the ability to control this feature for those cases when the user prefers manual control or uses specific accessories.
To access the required section, follow the following steps:
- 📱 Open the Settings app on the home screen or in the menu of all apps.
- 🔍 At the top of the screen, use the search bar and enter the query "sensor" or "approximation".
- 🖱️ Select the Approximation Sensor in the search results, which usually leads immediately to the desired switch.
- ✅ Activate the switchboard by moving it to the Included position.
If the search didn't work, the path might be through the call menu. Go to the Phone app (green handset), click on the three dots in the top right corner and select Settings. Next, go to Incoming Calls. That's where the Approximation Sensor option often hides, depending on the firmware version installed and the regional modification of the device.
Once the function is turned on, you need to make a test call. Hold your hand to the top of the screen during the beeps, the display should go out. If the screen continues to burn, then the software activation was successful, but additional calibration or check for physical obstacles is required.
Using the Engineering Menu for Diagnostics
When a standard switch is missing or not working, the CIT (Customer Integration Test) is a hidden part of the system designed to test hardware components in the factory, accessed on the Redmi Note 9 through a special code in the dialing application.
Open the Phone app and dial the combination ##6484##. Immediately after entering the last digit, the list of tests will open. Find the Proximity sensor item in the list (usually at the top or middle of the list), clicking on it, you will be in the testing mode, where you will see the current readings of the sensor.
In this mode, the screen can flash or show numerical values.
- 🖐️ If the value changes (for example, from 5.0 to 0.0 or the Pass sign appears), then the sensor is physically correct.
- 🚫 If there is no reaction, the problem may be in the hardware or a deep software driver failure.
- 🔄 In some versions CIT There is a Calibration button that allows you to reset the current readings to zero.
⚠️ Note: Do not change other parameters in the engineering menu unless you are sure of their purpose. recalibration of other sensors (accelerometer, gyroscope) may require a complex recovery procedure.
☑️ Checking in CIT menu
The engineering menu is a powerful tool to separate a software bug from a physical breakdown, and if the sensor is perfectly functional in CIT mode, but the screen doesn't go out in normal call mode, it means that some third-party application is in conflict or the system configuration files are lost.
Deep calibration through system code
Sometimes the sensor is on and physically functional, but it doesn't work properly because of the wrong thresholds. Xiaomi has a special service code that allows for forced calibration, a technique that often helps if the screen goes out too early or too late.
The calibration procedure is as follows:
- Dial ##855## in the dialing app, and this will open a hidden sensor calibration menu.
- In the list that opens, find the Proximity Sensor and click on it.
- Press the Calibrate button.
- Follow the on-screen instructions: You usually need to remove all items from the top of the phone and then close the sensor with your hand.
Once the procedure is completed, the Calibration Success message will appear on the screen. If you see a Fail, try again, making sure that the phone is on a flat surface and nothing interferes with the sensor. In some cases, you need to restart the device to take new parameters into effect.
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If calibration consistently gives an error, try to wipe the top of the screen with an alcohol wipe before starting the procedure to remove the fat film, which can distort the IR sensor readings.
This method overwrites a configuration file that stores the base values for the sensor, especially after a firmware update, when new algorithms may misinterpret old calibration data.
Influence of accessories and protective glasses
One of the most common reasons for the proximity sensor to malfunction on the Redmi Note 9 is security accessories. The design of the smartphone is such that the sensor is located very close to the edge of the speaker. Any thickening in this area can be a critical obstacle to infrared radiation.
Pay attention to the following factors:
- 🛡️ Black-framed protective glass: If the black edging of the glass covers the speaker area, the sensor can be completely locked. In this case, only replacing the glass with a model with a notch under the speaker or without a black bezel helps.
- 🧱 Thick cases: Some cases have high sides, which when pressed tightly against the ear of the phone can mechanically press on the sensor area or create a shadow.
- 💊 Speaker stickers: Popular dust-retardant nets, glued over the speaker, are often made of materials that are opaque to IR rays.
It's easy to check the effect of the accessory: remove the cover and the protective glass, then repeat the test call. If the problem is gone, the accessory is the cause. In the case of glass, sometimes neat scraping of the black paint in the sensor area helps, but this requires jewelry accuracy and can spoil the appearance of the protection.
| Accessory type | Probability of problem | Decision |
|---|---|---|
| Black-framed glass | Tall. | Replacement with transparent or cut-out |
| Dust netting | Medium | Removal or replacement by a more subtle |
| Thick silicone case | Low. | Removal of the cover during calls |
| Hydrogel film | Minimum | Normally not affecting work. |
Solving program conflicts and resetting
If neither calibration nor removal of accessories helped, there may have been a software failure in the system. Xiaomi has a system process that can freeze or conflict with applications that have access to the microphone and phone, and it is worth checking the application permissions first.
Go to Settings → Apps → All Apps. Find the Phone app (or Google Phone if you use it). Go to Permissions and make sure that access to the phone and microphone is active. Also try to clear the app's cache: press Memory → Clear cache. This won't delete your contacts, but will reset temporary files that may have been corrupted.
In extreme cases, if the problem is massive after the MIUI update, a full reset can help.The full reset (Wipe Data) removes all information from the phone, so be sure to back up contacts and photos before starting the procedure.
It is executed through the menu Advanced settings → Reset settings → Erase all data.
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If the sensor does not work even after resetting and in safe mode, there is a high probability of physical failure of the plume or the sensor itself, which requires replacement of the spare part.
Also worth mentioning is Safe Mode, if you have installed an app that intercepts calls (call recorder, number detector), it can block the regular sensor, try removing newly installed telephony apps and check the device's performance.