What a safety-number change actually signals
A safety number is a check on the security of a one-to-one conversation, not a check on who the other person is. That distinction matters when the number changes and Signal asks you to approve it.
Signal safety numbers help check the security of a one-to-one conversation; they do not verify the other person’s identity. Source
So treat the change as a prompt to verify the channel again, not as evidence that someone is impersonating your contact. The change tells you the security number no longer matches what you previously saw; it does not tell you why.
Two common reasons the number changes
A safety number may change for routine reasons. The most common are a new phone or a reinstallation of Signal. Neither requires an attacker, and neither is proof of one.
A safety number may change after a new phone or reinstallation; a changed previously verified number requires approval before sending a new message, and undelivered old messages are not resent. Source
If you had previously verified the number, Signal requires approval before a new message can be sent. That approval step is the moment to compare values rather than tap through.
Step by step: compare, then verify
Do the comparison in the chat where the request appears, then confirm the value through a separate channel you already trust — for example, a phone call or an in-person conversation, not the same chat you are checking.
- Open the one-to-one chat where the safety number changed.
- Go to the chat settings for that conversation and view the safety number.
- Compare the QR code or the numeric value with what your contact sees on their device, using a separate channel.
- Mark the number as verified only after the values match.
- If the values do not match, do not mark it verified; keep the conversation unresolved and investigate before sharing anything sensitive.
After accepting a message request, a user can view the safety number in chat settings, compare the QR code or numeric value, and mark it verified locally. Source
The exact menu labels in your app version may differ from the wording here. If you cannot find the safety number in chat settings, treat the comparison as unresolved rather than assuming a match.
If you cannot compare right now
Comparison is not always possible: your contact may be offline, may not have their device, or may not be able to read a value to you. In that case, the honest answer is that the result is unresolved.
- Do not mark the number verified just to clear the prompt.
- Do not treat the change as proof that your contact is untrustworthy or that their identity is confirmed.
- Do not send secrets, passwords or one-time codes as a “test” to see whether the contact is genuine. A reply does not prove identity, and the secret has already left your control.
- If you must continue the conversation, keep sensitive details out of it until you can compare through a separate channel.
Old undelivered messages are not resent
One practical consequence of a changed number is easy to miss: messages that were not delivered before the change are not automatically resent. If you expected a message to arrive and it did not, check with your contact rather than assuming it was delivered.
A safety number may change after a new phone or reinstallation; a changed previously verified number requires approval before sending a new message, and undelivered old messages are not resent. Source
This is a delivery detail, not a security verdict. It also means a silent gap in the conversation is not evidence of interception.
What this check does not do
A safety-number comparison verifies the security number for that conversation. It does not confirm that the person you are talking to is who they claim to be, and it does not audit their accounts elsewhere.
| Question | Does the safety number answer it? |
|---|---|
| Is this conversation using the number I last verified? | Yes, once you compare QR or numeric values |
| Is the person on the other end really my contact? | No |
| Was the change caused by an attacker? | No — a new phone or reinstallation can also cause it |
| Will old undelivered messages arrive after approval? | No, they are not automatically resent |
If your concern is about identity rather than the channel, a username search is a different task. TraceSeek checks public usernames across 3,000+ platforms, and the first scan is free with no registration or login required; a typical scan takes 20–30 seconds. A public match is a lead, not proof of ownership, and it does not control Signal settings, recover accounts or verify identity.
A related task: what you share before accepting
Approving a changed safety number is about an existing accepted conversation. A neighboring question is what to check before you accept a message request in the first place, especially when a stranger asks for profile details. That task is covered separately in the related account-control guide.
If you also want to see what your own public accounts reveal to others, the next useful read is review your public account footprint.