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Signal, the secure messaging application, ties itself to your phone number. For extra protection against thieves stealing your phone number, you can enable Registration Lock, preventing anyone from registering another account with your phone number.
What Is Registration Lock?
Your Signal account is tied to your phone number, which means you don't even need a password to log in. Your Signal account can only be linked to one phone number, so you can only have Signal active on one iPhone or Android smartphone at a time.
To sign up again on a new device, you'll need access to your number (usually via your SIM) so that you can receive a code to prove who you are. But what happens if someone steals your phone or your SIM, or gets access to the Google Voice or similar account you used to sign up?
Registration Lock prevents your account from being re-registered on another device without the PIN you used to sign up for Signal being provided. With Registration Lock enabled, whoever gets ahold of your SIM or Google Voice account will also need to know your PIN to use your account.
Signal will block your account for a week if you enter the wrong PIN a few times. If you forget your PIN, Registration Lock will expire seven days after inactivity (This is reset each time you access your Signal account from a linked device.).
Once Registration Lock has expired, you will be able to re-register your number without a PIN.
Enabling Registration Lock on Your Device
You can enable Registration Lock by launching Signal and tapping on your user icon in the top-left corner of the screen.
In the menu that appears, tap "Privacy" to reveal an additional list of options.
Under the Privacy menu, find and enable "Registration Lock." It's about halfway down the list.
If you want to reset your PIN, you can do so from this menu via the "Change Your PIN" option. You don't need to know what your PIN was to do this. Provided that your device is registered, Signal will let you change your PIN.
While it's unlikely that an intruder would be able to guess even a four-digit PIN before being locked out of your account, you can opt to create a more complex alphanumeric PIN (a password) by tapping the "Create Alphanumeric PIN" button in the "Change Your PIN" menu.
More Tips for Locking Down Signal
Even though Signal is focused on protecting user privacy, there's more to secure messaging than simply downloading the app. Find out how to properly lock down Signal to protect both your and your contacts' privacy.
If you use Signal for security purposes, you might want to learn a bit more about rival app Telegram, too.