How do I see which devices are signed in?

DeskOps does not list every signed-in session. Trusted devices shows the devices you chose to remember for 30 days after an email-code check (for example, before connecting a bank), each with a Revoke option. If you think someone else is signed in, use Sign Out All on the same screen — it ends every session on every device — and then sign back in on the devices you actually use.