There are a number of different types of 2FA including:
Tokens
This is a small device (that may, for example be attached as a key fob), which randomly generates a code via an LCD display that the user inputs into their access screen.
SMS
whereby a code can be sent to a recipient via mobile text.
Smart or Swipe Card
Where a card is used in a card reader in order to generate a code that can be input into the system to validate the users access.
CAPTCHA
These systems continually code characters on a web based system that a user will have to replicate in order to verify their identity.
Biometrics
Whereby an individual has to use their fingerprint in order to access systems. Retina recognition is also becoming more readily available. This is where a device is used to scan a person’s eye in order to verify whether they can have access.