Similar to when AIM notifies you that you're still logged in on another computer, Facebook will go even deeper and not only tell you how long you've been logged in for, but the name of the device and location too.
While the feature hasn't gone live yet, it's going to be so handy knowing where you are still logged in - and being able to sign off from there too. It will actually let you sign off from one or all of the locations, whether that be a phone, computer, tablet or TV. Keep an eye on the Account Security section of Facebook for when it goes live. [TG Daily]