How to detect new Machine like Facebook?

Question

I am actually trying to detect a person, using a computer, Just like facebook. Whenever you sign into facebook using different machine, it detects the new machine and asks you t

Answer 1

Facebook uses cookies to detect new devices. Deleting all cookies will lead Facebook to ask you to name your new device. Facebook has some tolerance for deleted cookies. For instance, deleting the long-living cookies has no effect if session cookies are set and you are already logged in.

In addition Facebook seems to use the IP to detect when the user logs in far away from their usual location.