Signal can only be used on one mobile device and up to five linked secondary devices. Currently supported linked secondary devices are iPads and computers.

If you've set up another device, follow steps to resolve for your platform:

Android

I set up Signal on another phone. How can I use Signal on this Android phone again?

Tap on the "Device no longer registered" banner to re-register Signal on your phone to make it the active device. After registering again, this phone will be connected and your other device will go offline.

My camera does not scan the QR code. What can I do?

Move your phone further away or closer to the code.
Increase the brightness of the monitor or laptop screen.
Resize the Signal Desktop window.

What if I see an error after scanning the QR code?

If you see Network Error,

Update to the latest version of Signal on your phone.
Confirm your Signal number is registered and you can send and receive Signal messages.
Install Signal Desktop again.

iOS

I want to copy my message history to my other device.

Account transfers move your account to the other device. Transfers move data to the new device which deletes it from the old device.
To use multiple devices, an iPad or Desktop must be linked as a new device. You have the option to synchronize the chats and 45 days of media existing on your phone to the linked device.

How can I use multiple devices?

To use multiple devices, an iPad or Desktop must be linked as a new device.
Make sure to select Add as New Device on the iPad to continue.

I don't want to link an iPad. How do I set it up as a separate device?

Follow steps on the support page to install as a separate device.

Why can't I link my iPad?

Update to the latest version of Signal on your phone.
There is a limit of 5 linked devices. Confirm you have not hit this limit.
Check firewall and network settings. If you have a VPN or firewall, make sure you allow *.signal.org and TCP port 443. The underlying IPs are constantly changing, so it'd be hard to define accurate firewall rules. If you have a transparent or reverse proxy it needs to support websockets.

I previously used an iPad as a separate device, how do I link that to my phone?

If your iPad is a linked device, transferring messages to a phone is not supported.
If your iPad was a separate device, follow the steps below.
1. Install Signal on your phone and complete an account and message transfer.
2. Reinstall Signal on your iPad which will clear your message history.
3. Link the iPad with your phone.
4. Your iPhone will have your message history and your iPad will not have any previous history.

What do I do if I see an alert or error after scanning the QR Code?

If you see QR Code Detected - No Usable Data Found, then you are scanning the QR code from an app that is not Signal.

In Signal, tap your profile > Settings > Linked Devices.
Select Link New Device and use your iPhone to scan the QR-code.

I set up Signal on another phone. How can I use Signal on this iPhone again?

Multiple phones are not supported. Tap on the "Device no longer registered" banner to re-register Signal on your phone to make it the active device. After registering again, this phone will be connected and your other device will go offline.

Desktop

I'm unable to link Signal Desktop. How do I resolve this?

Error	Troubleshooting Steps
"Signal cannot link this device using your current network."	Is your computer in a corporate environment/used for work? If so, attempt to log out of your corporate network. Ensure that security or antivirus software and other third-party programs installed on your computer are not preventing you from connecting to Signal servers. Check your VPN, firewall or proxy settings.
"The QR code couldn't load. Check your connection and try again."	Try disconnecting and reconnecting to your WiFi network, and quit and re-launch Signal Desktop.

Still not working?

Ensure you're running the latest version of Signal Desktop. You can download and install the latest version of Signal Desktop from https://signal.org/download.
Confirm you have not hit the limit of 5 linked devices per phone.