Want to know if someone is logged into your Facebook account without your permission? First, go to your settings page.
Under the Security folder, you'll see the link "Where You're Logged
In." Here you will find all your active Facebook log-ins from desktop or
mobile. It will (usually) provide data on the location, browser, and
device. If something seems fishy, you also have the ability to "end
activity" from individual or all devices.
This also comes in handy if you logged in to your friend's computer or on some public laptop, but forgot to log out.
This also comes in handy if you logged in to your friend's computer or on some public laptop, but forgot to log out.