How to Lock the Bootloader on a Samsung Galaxy S21: Step-by-Step Guide

Preparing Your Samsung Galaxy S21

• 💡 Ensure your device is running the stock ROM (official Samsung system) before proceeding.
• ⚠️ Remove any existing root access or third-party system modifications.
• 💾 Back up all your important data as this process will result in a factory reset.
• 🔌 Prepare a data-capable USB cable and a connected PC.

Locking the Bootloader

• 🔌 Power off your phone, then connect the USB cable while holding Volume Up + Volume Down buttons.
• ⬆️ Once the screen appears, hold the Volume Up button to confirm and initiate the "Lock bootloader" process.
• 💥 The phone will undergo a factory reset and data erasing process.

Post-Reset Setup and Security

• 📶 After the reset, complete the initial phone setup, including connecting to Wi-Fi.
• ⚙️ Navigate to Settings > About phone > Software information and tap Build number repeatedly to enable Developer options.
• 🔓 Within Developer options, verify that OEM unlocking is turned on.
• ⏸️ Go to Software update, connect to Samsung servers, and pause any detected updates.
• 🔒 Return to Developer options, turn off OEM unlocking, and restart the phone.
• ✅ Upon restart, re-enable Developer options to confirm that OEM unlocking is off and the device is secured with Device Protection.