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I've always thought that if a device is unlocked it means that it works with different carriers. If the device bootloader is unlocked, then does this mean the device will automatically work with different carriers? That is do unlocked device and unlocked bootloader mean the same thing?

All I know is that an unlocked bootloader is easier to root as commands can be sent to the device using the fastboot protocol used to boot it so it is not necessary to take advantage of an exploit on the device in order to root it.

I want to know if unlocked device and unlocked bootloader are synonymous.

Thanks.

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No, they're completely unrelated things. As you say, an unlocked device means it's not locked to a particular carrier: you can insert a different SIM card to change to a different carrier, and it will work. A locked device will not connect to another carrier if you change the SIM card.

The bootloader is the first thing that runs when you turn the phone on: it's responsible for loading the core Android code, so that Android can load itself and run. A locked bootloader uses digital signatures to verify the Android code it's loading, which means it will only boot a ROM (firmware image) that's signed by the device manufacturer. In contrast, an unlocked bootloader will load any ROM. Unlocking a locked bootloader will wipe all user data (but not the ROM) from the device. This is a security mechanism, so you can't get at the data on a phone by installing your own ROM on it.

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  • @jiggunjer No, the stock ROM isn't erased, just the user data, like a factory reset. Thanks for letting me know the answer wasn't clear.
    – Dan Hulme
    Commented Nov 2, 2015 at 23:10
  • One more point that isn't clear to me: if you manage to flash an unsigned ROM on a bootlocked device, what will happen? bootloop? some error screen? stuck in the recovery?
    – jiggunjer
    Commented Nov 3, 2015 at 0:58
  • @jiggunjer I believe it will get stuck in the recovery, but I've never seen it myself. If you really want to know you should ask a new question.
    – Dan Hulme
    Commented Nov 3, 2015 at 8:13
  • @DanHulme It will be stuck at the bootloader telling your device is corrupt (and refuses to boot). Actuallt I quite doubt you can flash an unsigned ROM without unlocking BL first.
    – iBug
    Commented Jan 1, 2018 at 2:13
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The term "unlocked device" is as confusing as the term "ROM" (see the tags tag wiki). Only from the context one can tell whether it refers to "a device with an unlocked bootloader", or "a device without network/SIM lock".

This means, your question cannot be answered with a simple "Yes" or "No": though the terms are used as synonyms, "unlocked device" stays ambiguous without proper context. But it's quite more likely that "unlocked device" refers to the "network/SIM lock".

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Just a precision, to be clear: bootloader-unlocking does NOT network-unlock a device. It also voids the warranty and stops any DRM'ed video/music/app from playing/working.

Lots of good explanations here: http://forum.xda-developers.com/showthread.php?t=1839477

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