I have not logged out of FB and logged back in (ie, not there and then, always every 2 days or so), but over lets say a week, and its the same laptop, if I log into FB, and nothing else has changed, FB's system views it as a new device, and says so, "it looks like you are logging in from a new device", and says, "please enter the 6 digit code that has been sent to your mobile device", and sure enough, my mobile will pling with the 6 digit code.
FB is being safe, better than being sorry and losing all my FB points/VFF points to some scammer somewhere.
QF/QFF/QFmoney on the newer smart phones, will now ask you to log in with your pointy finger on the sensor on the back of the phone.
Even WWR is now sending out 2fa 6 digit codes to mobiles now too.
Which is a good thing.
FB could go the pointy finger route of finger print scanning, but as of now, they are not doing it.