Yes, you can use the same Session ID on multiple devices.
To log into an existing Session ID on desktop:
- Download and install Session on your new computer
- Open the Session app, but instead of creating a new Session ID, click Sign In
- Click Restore from Recovery Phrase
- Enter your recovery phrase into the text field provided and choose your nickname
- Done!
To log into an existing Session ID on mobile:
- Download and install Session on your new device
- Open the Session app, but instead of creating a new Session ID, tap Continue your Session
- Enter your recovery phrase into the text field provided
- Enter your nickname and tap Continue
- Done!
Your additional device should now sync with your first device, and both devices should be able to send and receive messages from the same Session ID.