How does security Device work? The one that apparently generates random numbers to login to your office networ

Update: Its not about IP. Let me explain. To connect from home to my office network. I have a small digital device- that shows up - 8 digit-numbers (on LCD display) - so, whenever I connect from home to office network. I will require to - put the password and this number. In another case, I need a similar no. to login to... show more Its not about IP. Let me explain. To connect from home to my office network. I have a small digital device- that shows up - 8 digit-numbers (on LCD display) - so, whenever I connect from home to office network. I will require to - put the password and this number. In another case, I need a similar no. to login to my bank a/c. Its like an added security. But question is: How does this device work? Do they have satellite access or a mini- pseudo-random generator.
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