How to turn on the proximity sensor on Xiaomi Redmi 9T: a complete guide with a health check

The proximity sensor in Xiaomi Redmi 9T smartphones is a small but critical element that is responsible for automatically locking the screen during phone conversations. Without it working correctly, you risk accidentally pressing buttons with your cheek or ear, interrupting the call or activating speakerphone communication. However, many users do not even know about the existence of this sensor until they encounter problems: the screen does not go out when the phone is held to the ear, the sensor continues to respond to touch, or, on the contrary, the sensor works too early, interfering with control.

In this article, we'll look at all the ways that the Redmi 9T's proximity sensor can be turned on and configured, including hidden developer settings, checks through the engineering menu, and troubleshooting. We'll focus on the difference between the proximity sensor and the light sensor, which are often confused, although they have fundamentally different functions. If your smartphone is acting strangely during calls, this instruction will help to get things back to normal.

Note: Redmi 9T (codenamed lime) has an infrared proximity sensor that is located next to the front camera, and it depends not only on the hardware settings, but also on the MIUI firmware version. If you recently upgraded the system, some parameters may have reset to factory values.

What is a proximity sensor and why you need it

The proximity sensor is an optical sensor that detects the distance between a smartphone screen and an object (like your ear while you're ringing), and its primary purpose is to prevent accidental tapping of the display when the phone is pressed against your head. Without this mechanism, you could:

• 📞 Interrupt the call with the "Out" button"
• 🔊 Turn on the cheek speaker
• 📱 Activate other touch screen functions

On the Redmi 9T, the sensor is paired with a software algorithm that analyzes data and locks the screen when a nearby object is detected. It's important to understand that it's not the same as the light sensor (it adjusts the brightness of the screen), both of which are located side by side, but they perform different functions.

Interesting fact: in some MIUI firmware, the proximity sensor is also used to save battery power, for example, if you put your phone down on the table with the screen, the system may turn off the backlight of the display earlier than usual, believing that the device is not in use.

Where is the proximity sensor on the Redmi 9T

On the Xiaomi Redmi 9T, the proximity sensor is located at the top of the screen, to the right of the front camera, and visually it can be detected by a small circular hole next to the speaker. If you look closely, you'll see two sensors:

• 🔦 Proximation sensor (infrared)
• 🌞 Light sensor (photocell)

To accurately identify the proximity sensor, you can use a flashlight: hold the light source to the top panel, the light sensor will respond to the change in the brightness of the screen, and the proximity sensor will remain neutral. You can also try to close the hole with your finger during the call: if the screen goes out, then the sensor is healthy.

On some Redmi models, the proximity sensor can be hidden under a protective glass, which makes it difficult to visually inspect, in which case you will have to use software methods to test the performance, which we will discuss later.

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If your Redmi 9T has a protective film or glass installed, make sure it doesn’t cover the sensor area, and even a slight shift can cause sensors to malfunction.

How to turn on the proximity sensor through the MIUI settings

In most cases, the proximity sensor on the Redmi 9T is activated by default, but sometimes it can be disrupted due to system failures or incorrect settings. To make sure the sensor is on, follow the following steps:

Instructions for activation:

1. Open the Settings app (cog icon).
2. Go to the System and Device section → Additional settings.
3. Select the screen lock option during the call.
4. Make sure that the approach sensor slider is in the On position.

If this item is not in your version of MIUI, then the setting is controlled at the firmware level and does not require manual activation, in which case, check the sensor through the engineering menu (instructions in the next section).

Also note the Auto Lock setting in the Screen section. If it is disabled, the proximity sensor may not work properly, as the system will not block the display when you hold the phone to your ear.

Whether "Settings" are open → System and device"?

Is the "Screen Lock During Call" option activated?

Is the Approach Sensor Slider on?

Checked if the setting "Automatic lock" in the "Screen" section"?-->

Checking the proximity sensor through the engineering menu

If standard settings fail, you can test the proximity sensor through a hidden engineering menu, which allows you to get accurate data about the operation of the sensor and detect hardware malfunctions.

How to open the engineering menu:

1. Open the Phone app.
2. Enter the combination: ##6484### (or #4636## for older versions of MIUI).
3. Select the Hardware Testing option → Sensor Test.
4. Find the Proximity Sensor string.

In normal condition, when you hold your hand to the top of the screen, the value should change from 5.00 (no obstruction) to 0.00 (object detected). If the numbers do not change or the sensor shows N/A, this indicates:

• ⚠️ Hardware malfunction of the sensor
• ⚠️ Contamination or damage to the protective glass
• ⚠️ Software glitch in firmware

For more detailed diagnostics, you can use apps from Google Play, such as Sensor Test or Phone Doctor Plus, which provide advanced information about all the sensors of the smartphone.

Setup of the proximity sensor through the developer parameters

In some cases, standard settings don't allow you to fine-tune the sensor, so the developer's settings come to the rescue, where you can change the threshold of the sensor's operation or force it to turn off.

How to activate the developer parameters:

1. Go to Settings. → The phone.
2. Find the MIUI version string and tap it 7 times in a row.
3. Enter a pattern lock or password if required.
4. Return to the main settings menu – a new item for developers will appear.

Now find in the developer parameters the following options related to the proximity sensor:

• 🔧 Disable the proximity sensor (should be turned off)
• 📏 The threshold of the proximity sensor response (default value: 5.0)
• 🔄 Reset sensor settings (in handy if the sensor is unstable)

Important: changing the trigger threshold can lead to false positives or, conversely, to ignoring close objects. The optimal value for Redmi 9T is from 3.0 to 5.0. If you are not sure of your actions, you should leave the default settings.

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The developer's settings allow you to flexibly adjust the proximity sensor, but the wrong values can make it worse. If the sensor stops functioning properly after the changes, reset the sensors.

Frequent proximity sensor problems and their solutions

Even if the sensor is on, it can be incorrect, and let's look at the typical faults and how to fix them.

Problem 1: The screen does not go out during the call

• 🔹 Check if the sensor is covered with dirt, film or cover.
• 🔹 Make sure that the call settings do not turn off the screen lock option.
• 🔹 Update the firmware MIUI last-minute.

Problem 2: The sensor is activated too early

• 🔹 Reduce the trigger threshold in the developer settings (e.g., from 5.0 to 4.0).
• 🔹 Check if the sensor is disturbed by a magnetic or metal case.
• 🔹 Calibrate the sensor through the engineering menu.

Problem 3: The sensor doesn't respond at all

• 🔹 Reboot your smartphone – sometimes a simple reboot helps.
• 🔹 Reset sensor settings in developer settings.
• 🔹 If nothing helps, contact the service center - a hardware breakdown is possible.

If the problem persists after all the manipulations, try rolling back the firmware to the previous version or performing a full reset (don’t forget to back up the data!).

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Before visiting the service center, try to test the sensor in safe mode (Plug the power button → Reboot in safe mode). If the sensor is working properly, one of the installed applications is to blame.

How to Calibrate the Approach Sensor on Redmi 9T

Calibration of the proximity sensor may be required after a firmware update, a drop in the phone, or prolonged use, a process that helps reset the sensor’s current settings and return it to factory settings.

Method 1: Through the Engineering Menu

1. Open the engineering menu (combination ##6484##).
2. Go to Sensor Test. → Proximity Sensor.
3. Press Calibrate and follow the instructions on the screen.
4. Once completed, restart the phone.

Method 2: Through the Developer's Parameters

1. Open the Settings. → For developers.
2. Find the item Reset sensor settings.
3. Confirm the action and wait for the process to be completed.

After calibration, check the sensor during the test call. If the problem persists, you may need to flash the device or replace the sensor.

Critical information: In some versions of MIUI, the proximity sensor calibration may reset the light sensor settings. After the procedure, check for automatic brightness adjustment.

FAQ: Answers to Frequent Questions About the Approach Sensor