Devices & Sessions
You can see everywhere your account is signed in, and end those sessions if something looks wrong.
Viewing your devices
Open Security in Settings. Each entry is a device — the browser it is using, where it was connecting from, and when it was last active. The one you are reading this on is marked so you can tell it apart.
Devices are grouped rather than listed one line per sign-in, so a computer you have logged into several times appears once, with its most recent activity, instead of filling the list.
Take a moment over anything you do not recognise. An unfamiliar browser or a location you have never been to is the thing this page exists to show you.
Signing out everywhere
Sign out of all devices ends every session at once, including the one you are using. You will be asked to sign in again immediately.
That is deliberate. If someone else has been in your account, a sign-out that spared the browser they were sitting at would have achieved nothing.
It also takes effect immediately rather than whenever sessions would have run out on their own — there is no window in which someone already signed in keeps working for a few more minutes.
It is all or nothing: there is no way to sign out one device and leave the others.
If you think someone has your password
Change your password rather than only signing out.
Changing it ends every other session in exactly the same way — anyone signed in elsewhere is thrown out at once — and it also removes the thing that let them in. You stay signed in on the device you changed it from, so it costs you nothing.
Signing out everywhere on its own leaves them able to sign straight back in with the password they already know. Changing the password does both jobs, which is why it is the better first move whenever you are worried rather than just tidying up.
Staying signed in
Sessions last about half a day of inactivity. Using the dashboard keeps yours alive, so you will not be interrupted mid-task; leave it overnight and you will be asked to sign in again in the morning.
That is a security measure rather than an inconvenience — a dashboard left open on a laptop in a café should not stay open forever.