With safety numbers on Signal, you can check whether the person you are chatting with is really the person you think you are chatting with. This does not confirm anyone’s identity, but rather the security of the connection between two accounts.
If the safety number you see in a particular chat matches the safety number your contact sees for your chat, then you know the messages are truly reaching each other’s devices, and not the phone of a hacker (man-in-the-middle attacks).
The safety number usually also changes when someone gets a new phone or reinstalls Signal. So a change in the safety number does not automatically mean you have been hacked. However, if a safety number changes frequently or unexpectedly, something may be going on.
Read more about safety numbers in our Signal Security & Privacy Guide.
