Facebook told the service is designed to help users to keep their logins secure. Users can enjoy this new service within two weeks. The new service is available for computer users only, but not on mobile devices.
For using this service, the users have to go to 'account settings' on the Facebook page and click on 'change' next to 'account security.' There, the users can see where else the Facebook account is logged in, including the type of device and the city it's in or near. To log out of any of them, users have to click 'end activity.'