To solve the above problem, Signal supports a feature called Registration lock, which prevents anyone else from being able to register for the Signal account with your phone number.
What is Registration Lock?
With that said, your Signal account will be closely linked to your phone number. Meaning you don’t even need a password to login. However, your Signal account will only be able to be linked to a single phone number, so you will also only be able to activate Signal on one iPhone or Android smartphone at a time. .
To re-register on a new device, you will need access to your phone number (usually via SIM) in order to be able to receive a verification code. But what if someone steals your phone or SIM, or has access to Google Voice and the same account you used to sign up for Signal account?
The Registration Lock is to prevent your account from being re-registered on another device without the PIN you used to register for Signal provided. Once the Registration Lock is activated, anyone who holds the SIM or your Google Voice account will still need a PIN to be able to access and use the respective Signal account.
Signal will lock your account for a week if you enter the wrong PIN a few times. In case you forget your PIN, the Registration Lock will expire seven days from the point of inactivity. (This is reset every time you access your Signal account from a linked device.).
Once the Registration Lock expires, you will be able to re-register your phone number without providing a PIN.
How to enable Registration Lock in Signal
First, launch the Signal app on your phone and tap on your user icon in the top left corner of the screen.
In the menu that appears, click “Privacy” to display a list of additional options.
In the “Privacy” menu, find and enable the “Registration Lock” option. This option is somewhere in the middle of the list.
Alternatively, you can reset your PIN right in this menu through the option “Change Your PIN”. You can reset without knowing what your PIN is, but provided your device is registered.
You can choose to create a more complex alphanumeric PIN by clicking the “Create Alphanumeric PIN” button in the “Change Your PIN” menu.