Before relocking an Android bootloader, make sure the phone is running software the manufacturer accepts for that exact model, back up your data, and follow the manufacturer’s current instructions. Relocking makes the bootloader verify the operating system against a trusted root of trust. If the installed software is modified or unsupported, verification can fail and the phone may not boot. These checks reduce avoidable risk; they cannot guarantee a device will never become unbootable.
Why the software state matters before relocking
An unlocked bootloader can allow software that is not signed by the device’s trusted root of trust to start. When the bootloader is locked, Android’s verified-boot process checks that the operating system is trusted and unmodified. If the phone contains a custom ROM, patched boot image, modified recovery, or mismatched firmware, it may fail that check after relocking.
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Only relock when the device is in a manufacturer-approved state, or when the manufacturer or ROM project explicitly documents a supported signed-key relock path for your exact device and configuration. A build that merely boots while unlocked is not proof that it will pass verification while locked. AOSP describes the relationship between device state and verified boot in its Device state documentation.
Preflight checklist: what to do before you relock
- Identify the exact device and build. Record the phone’s model, regional variant, Android version, and current build number. Firmware and locking instructions can differ between variants of the same phone.
- Find the current official instructions. Read the manufacturer’s relocking and firmware-restoration directions for that exact model and build. Do not assume a generic Android command or a guide for a similar phone applies.
- Back up data and prepare for a reset. A device-state transition can wipe data. AOSP says transitions wipe data partitions, and Google warns that manually locking a Pixel may require a factory reset. Save files and confirm you can restore accounts and other important data before proceeding. See AOSP’s Lock and unlock the bootloader instructions.
- Restore all relevant software components. Return firmware and partitions to the vendor-approved state for your model. Remove root, patched images, custom recovery, and unsupported ROM components unless a documented signed-root workflow specifically supports them.
- Confirm the phone boots and passes the available verification check. Use the manufacturer’s verification method to confirm the expected trusted state. A successful boot while unlocked alone is not enough.
- Check anti-rollback and boot-slot instructions. Follow any model- and build-specific firmware sequencing directions before locking. These precautions can change with security updates.
- Use only the exact relock procedure for your device. Stay with the phone, read and confirm its on-screen prompt, and let the operation finish without interruption. Afterward, check that it boots normally and reports the expected locked and verified state.
Do not run a relock command, flash a package, or attempt a rollback based only on a general guide when the phone model and installed build have not been identified.
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Why a generic fastboot command is not a universal recipe
AOSP documents fastboot flashing lock as a generic command for locking the bootloader and resetting the device. That documentation does not establish that every manufacturer, model, or firmware version uses the same command or sequence. AOSP’s instruction is to “lock the bootloader and reset the device” with that command; use it only if the instructions for your exact device call for it.
Before acting, get the current procedure from the manufacturer for the precise model, regional variant, and installed build. If those instructions are unavailable or do not clearly cover your configuration, do not guess at a command or firmware sequence.
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Pixel-specific checks and update cautions
The following details apply to Pixel devices, not to Android phones generally. Google’s Verify your Android operating system page describes Pixel verification results. “Locked” under the Bootloader check needs no further action; an “Unlocked” result can be manually locked, but Google warns that a factory reset may be required. For Boot state, “Verified” means the OS is official and unmodified. “Self-signed” indicates a custom signing key, and “Failed” means the OS is corrupted. Google directs users who need repair toward a Google-approved public build or the Pixel Repair tool.
Google’s Factory Images for Nexus and Pixel Devices page says factory images restore original factory firmware, but a full OTA image is typically easier and safer to sideload. Factory-image installation erases data. Google recommends relocking after factory-image work is complete. The page was last updated 2026-10-06 UTC; check it again immediately before acting because its model-specific instructions can change.
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Pixel anti-rollback precautions are tied to particular releases
- For Pixel 6, Pixel 6 Pro, Pixel 6a, Pixel 8, Pixel 8 Pro, and Pixel 8a, Google says the May 2025 Android 15 update raises the bootloader anti-rollback version. Affected devices cannot flash and boot older Android 15 builds afterward. Google’s instructions say to update and boot the release, then sideload the corresponding full OTA and reboot so both slots have a bootable image.
- For Pixel 10, Pixel 10 Pro, Pixel 10 Pro XL, and Pixel 10 Pro Fold, Google says the May 2026 Android 16 update raises the anti-rollback version. Google warns that falling back to an inactive slot with an older bootloader can leave the device unbootable. Follow the current page’s instructions for the affected model and build before flashing.
These are release-specific Google instructions, not general Android rules. Do not apply them to another phone or build by analogy.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.If the device is already modified or verification fails
Do not relock while the phone is running unsupported software or reports an unexpected verification state. Restore a manufacturer-approved build using the exact device-specific directions first. On a Pixel, a “Self-signed” or “Failed” Boot state is not the “Verified” state Google describes for an official, unmodified OS; consult Google’s repair or public-build options rather than locking on the assumption that a custom or corrupted build will pass.
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If the phone no longer boots, avoid repeating relock or flash attempts with instructions for another model. Use the manufacturer’s recovery or repair guidance for the exact device and firmware state.
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