Does Signal send my number to my contacts?
Signal does not send your phone number to anyone unless you send them a message. The Signal service does not have any knowledge of your contacts. Data is all owned by your phone. Registration notifications are never transmitted by anyone in any direction at all; these notifications are created by your phone.
How does Signal know my contact is using Signal?
Signal periodically sends truncated cryptographically hashed phone numbers for contact discovery. Additionally, all connections to our servers are fully encrypted. Names are never transmitted, and the information is not stored on our servers. The server responds with the contacts that are Signal users and then immediately discards this information. Your phone now knows which of your contacts is a Signal user and notifies you if your contact just started using Signal.
Why did someone see that I joined Signal?
People who already know your number and already have you in their contacts see that they can contact you on Signal. Nothing is sent to them by your Signal app or the Signal service. They just see a number they know is registered. If someone knows how to send you an SMS, we want them to see that they can send you a Signal message instead.
Why did I see that my contact joined Signal?
You are notified when someone that is stored in your contact list is a new Signal user. If you can send an SMS to a contact, we want you to know you can send a Signal message instead. You can disable these alerts on your Android phone by going to Settings > Notifications > scroll to events and disable Contact joined Signal.
How do I know a contact is using Signal?
On Android, when looking at your contact list within Signal, a blue letter in the outside column will indicate it is a Signal contact.
- Go to the main conversation view.
- Tap on the message compose icon to view your Signal contact list.
- Pull down on your contact list to refresh.
- Look for the first letter of your contact in the left column. If the initial is blue, this is a Signal contact.
Learn how to know if your message is private on Android, how to know if your message is private on the iPhone (spoiler: it always is), about blocking contacts on Android, more about encryption that makes Signal private, or more about responses to government requests.