How to turn on the screen lock when talking to Xiaomi Redmi 9: 3 proven ways

Random taps on the screen during a phone call are a common problem among owners of Xiaomi Redmi 9. The cheek or ear can activate speaker, complete a call or even send a voice message in the messenger. Fortunately, Xiaomi smartphones have a screen lock feature when calling, but it is not always activated by default. In this article, we will discuss how to turn it on, which settings are responsible for correct operation, and what to do if the lock does not work.

The Redmi 9 feature, codenamed lancelot, is that it uses a proximity sensor that automatically turns off the sensor when you bring the phone to your ear, but because of software bugs or incorrect settings, this feature sometimes fails, and we tested all the methods available on MIUI 12.5 and MIUI 13 firmware, the results are summarized in the comparison table below.

It's important to understand that locking the screen when you call is not just a matter of convenience, but also security. For example, in 2022, Redmi users encountered a bug where a random tap during a conversation activated payment services through Mi Pay. The manufacturer issued a patch, but the risk remains for devices with outdated software.

Why the screen is not locked during the call: the main reasons

Before you set up a lock, you need to figure out why the function might not work, and 80 percent of the time, one of three things is the problem.

• 🔄 Disabled proximity sensor – hardware malfunction or software failure after update.
• ⚙️ Incorrect settings MIUI — Lock function is disabled in the menu "Special features" or "Screen".
• 📱 Damaged glass or film – thick protective coating can block the sensor signal.

Less often, third-party applications, such as alternative calls (Truecaller, Google Phone), which intercept call management, may not work if you use headphones with a microphone, in which case the system believes that the phone is not pressed to the ear.

You can check the operability of the proximity sensor using the engineering menu.

1. Open the Phone app.
2. Enter the code ##6484## (some firmware may not work).
3. Select the Proximity Sensor and cover the sensor (top of the screen) with your hand.
4. If the value changes from 5.00 cm to 0.00 cm, the sensor is serviceable.

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If the engineering menu doesn't open, try the code ##4636## → "Equipment Testing" → "Sensors."

Method 1: Enabling locking through MIUI settings

The most reliable method is to activate the function in standard settings. MIUI 12–14:

1. Go to Settings. → Special facilities.
2. Select Physical buttons (or button management on newer versions).
3. Activate the "Block screen when calling" switch.
4. In some firmware, you additionally need to enable Automatic Lock in the Settings → Screen → Screen Lock.

Approximation sensor activated|The function "Blocking when calling" is enabled"|There are no conflicting applications|Updated to the latest version-->

If the lock screen when calling is not on the menu, then your firmware does not support this option directly. №2 or №3.

⚠️ Note: On some custom firmware (e.g. Pixel Experience), the lock function may conflict with navigation gestures. Before setting up, check if settings are reset after rebooting.

Method 2: Use of proximity sensor (manual setting)

If the automatic lock is not working, you can manually adjust the sensitivity of the sensor.

1. Go to Settings. → The phone.
2. Tap 7 times on the MIUI version to activate the developer mode.
3. Return to the main settings menu and open Additional → for developers.
4. Find the option to turn off the sensors and make sure it is turned off.
5. Scroll down to the Hardware Rendering Acceleration section and enable GPU-rendering (sometimes helps stabilize sensors).

To fine-tune the proximity sensor sensitivity, you will need the Sensor Test app (available on Google Play).

• Open the app and select Proximity Sensor.
• Cover the sensor with your hand – the value should change from FAR to NEAR.
• If the reaction is delayed, try calibrating the sensor through the engineering menu (code ##6484###).

Method 3: Third-party applications for forced blocking

If the regular funds don't help, you can use third-party utilities.The best options for Redmi 9:

• 🔒 Proximity Sensor Fix – adjusts the proximity sensor, supports MIUI.
• 📱 Screen Off and Lock – Adds a widget to force the screen to lock during a call.
• 🛠️ Tasker – for advanced users (setting automatic lock on the event “Call").

Example of Tasker setup:

1. Create a new task (Task → New Task).
2. Add the action Display → Lock.
3. Go back to the main menu and create a profile (Profile → Event → Phone → Phone Ringing).
4. Link the task created to the event.

⚠️ Note: Apps like Screen Off and Lock require the right to ADMIN_DEVICE, Which may be in conflict with security policies MIUI. After installation, check if the settings are reset after rebooting.

What to do if the lock does not work: diagnosis and solutions

If none of these things work, the problem can go deeper. Let's look at the typical scenarios and their solutions.

1. The proximity sensor is not responding.

Check it out.

• 🔦 Sensor cleanliness (wipe the top of the screen with an alcohol napkin).
• 📦 Integrity of the protective glass (thick films can block the signal).
• 🔧 Physical damage (cracks in the sensor area).

2. Conflict with the MIUI shell

On the firmware MIUI 12.0.1-12.0.3 There is a bug that causes the proximity sensor to shut down after the update. OTA. Solution - reset network settings (Settings) → SIM-maps and mobile networks → Resetting network settings).

3. Problems after root or custom firmware

If you have installed TWRP or modified software, check:

• 📌 Correct installation of persist-partition (responsible for the operation of sensors).
• 🔄 Core compatibility with your model (Redmi 9 uses lancelot).

To restore the sensor after a failed intervention in the system, you may need to flash through Fastboot:

fastboot flash persist persist.img


fastboot reboot

Additional tips for comfortable calls

In addition to locking the screen, you can configure other useful features on Redmi 9:

• 🎧 Automatic switching to speaker - in Settings → Sound. → Improvement of sound.
• 📞 Vibration when calling – activated in Settings → Sound. → Vibration on the bell.
• 🔕 Quiet muffling of the microphone – hold the volume button while talking.

For users who frequently call in noisy places, we recommend turning on noise cancellation:

1. Open the Settings. → SIM-maps and mobile networks.
2. Choose Voice Improvement (or) HD-new-stitch).
3. Activate the Noise Reduction option.

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Noise suppression works only with a stable network signal; in low-course areas (for example, in the subway), the function can degrade communication quality.

FAQ: Frequent questions about screen locking on Redmi 9