Debugging by USB on Xiaomi Redmi Note 9: how to turn on and configure

Why do I need USB debugging on Redmi Note 9?

Debugging mode by USB (USB Debugging is a hidden Android feature that unlocks access to the advanced capabilities of the smartphone through a computer.On Xiaomi Redmi Note 9 (models) M2003J15SS, M2003J15SC etc.) this mode is required to perform operations not available in the standard interface MIUI. Without it, it is impossible to flash the device through fastboot, get root rights, use tools like ADB Scrcpy to manage your phone with a PC.

Enabling debugging over USB is the first step to:

• 🔧 Installation of custom firmware (LineageOS, Pixel Experience)
• 📱 Unlock the bootloader unlock via Mi Unlock Tool
• 🖥️ Controlling a smartphone from a computer (for example, to stream a screen)
• 🛠️ Data recovery after system failure

But it's important to understand that activating this mode reduces the security of the device, and through the open ADB port, attackers can access personal data if the phone is connected to an unsecured PC, so only enable debugging when necessary and disable it after use.

Preparation: Unlocking the Developer Menu

On the Redmi Note 9 (as with all Xiaomi smartphones), the USB debugging option is hidden in the Developer Menu. To unlock it, follow the following steps:

1. Open the Settings. → The phone.
2. Find the MIUI version string and tap it 7 times in a row.
3. After the notification “You became a developer!” appears, return to the main settings menu.

Now a new section Additional → For Developers will appear in the settings, and if it is not available, check if it is hidden in the Advanced Settings submenu (depending on the version of MIUI).

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On some Xiaomi firmware, the developer menu may be called “Developer Mode” or “Developer Settings.” If you don’t find it, search by settings (the magnifying icon at the top).

⚠️ Attention: Redmi Note 9 with MIUI 12.5+ After unlocking the developer menu, you may need to enter a password from the Mi Account. This is a security measure - without a tied Xiaomi account, some options will not be available.

Step-by-step: how to enable debugging by USB

Once the developer menu is activated, we go directly to debugging. Follow the instructions carefully - skipping steps can lead to errors when connecting to the PC.

Detailed sequence of actions:

1. Go to Settings. → Additionally. → For developers. ⚠️ Note: If the option is to debug USB Inactive (grey), first switch on the unlock switch OEM On some Xiaomi firmware, it blocks debugging access.
2. Find the USB Debugging option and move the slider to the right, and a warning will appear, press OK.
3. Connect the Redmi Note 9 to your computer via the original cable (it is advisable to use a USB 2.0 port for stability).
4. On the phone screen, a request will appear "Allow debugging over USB?" with an RSA key. Check Always allow from this computer and click Allow.

Critical detail: If you connect the phone to a new PC, the RSA request will pop up again. Xiaomi resets the list of trusted devices after resetting settings or updating MIUI.

Checking the work of debugging: ADB teams

To make sure that the USB debugging is working correctly, check through the command line.

1. Download and install Android SDK Platform-Tools (or use Xiaomi’s Mi Flash Tool).
2. Connect Redmi Note 9 to your PC and open Command Prompt (Windows) or Terminal (macOS/Linux) in the folder with adb.exe.
3. Enter the command: Adb devices

If debugging is enabled correctly, you will see the serial number of the device (for example, 1234abcd device) in the answer. If it appears unauthorized instead, you have not confirmed the RSA request on the phone or are using a non-original cable.

Security: Risks and how to minimize them

USB debugging gives you full control over your device via ADB, which means that any application or script on a connected PC can:

• 📁 Copy your files (photos, messages, passwords)
• 🔄 Install/remove programs without your knowledge
• 🔓 Bypass the screen lock (on some firmware)

To protect the data:

• 🔒 Use debugging only on trusted computers.
• 🔄 Turn it off after the work is completed (Settings) → For developers → Debugging by USB).
• 🛡️ Set a password to your Mi Account and enable two-factor authentication.

On the Redmi Note 9 with MIUI 13+ Xiaomi added additional protection: when connecting to a new PC, the system requires input PIN-The phone code, even if debugging is already allowed, prevents unauthorized access through the phone. USB.

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Never connect a USB debugging phone to public charging stations (airports, cafes) because they can steal data or install malware.

Frequent mistakes and their solutions

Even after debugging is enabled correctly, Redmi Note 9 users are facing problems. Let's look at typical scenarios and how to fix them.

1.The phone is not detected in fastboot

If you try to go to fastboot mode (holding Power + Volume Down), the computer does not see the device:

• Check if you have installed Mi Fastboot drivers (you can download from the official Xiaomi website).
• Try another one. USB-port (preferably) USB 2.0).
• Turn off all others. USB-PC devices – they can conflict.

Error "ADB server didn't ACK"

This error occurs when port 5037 is occupied by another process.

1. Close all programs that use ADB (such as Scrcpy or Android Studio).
2. Execute in command line: adb kill-server adb start-server

3. Hanging in the "Waiting for device" stage

If the adb device command does not show the device for a long time:

• Restart the phone and PC.
• Try another one. USB-cable (preferably original from Xiaomi).
• Disable the antivirus – it can block the ADB connection.

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Windows. 10/11 Sometimes, it helps to turn off the Quick Start function in the power settings. USB-port.

Disabling debugging over USB: when and how

USB debugging should be deactivated in the following cases:

• 🔌 After completing all manipulations with the phone (firmware, backup, etc.).
• 🛡️ Before transferring the phone to third parties (for example, to a service center).
• 📱 If you notice suspicious activity (independent application installation, traffic consumption).

To disable debugging:

1. Go to Settings → Additional → For developers.
2. Find the USB Debugging option and move the slider to the left.
3. (Optional) Disable the developer menu completely by resetting the settings in the Apps → All Apps → Settings → Storage → Reset.

⚠️ Note: On some versions MIUI After debugging is disabled, it may be necessary to restart the phone to make the changes take effect. ADB until next connection.

FAQ: Answers to popular questions