Some cards don't have any form of security. For example Konami "e-amusement" cards are just an ID number, which is also written on the back of the card. It is a username so to speak, the password is the PIN you enter when you start the game.

Some cards use some kind of challenge-response but are weak and are easily crackable.

Some cards have an anti-copy protection based on rolling codes, be careful with these. The idea is that when you use it to, say, open a door, the card sends a code to the reader and if correct, that code is burned and the reader replies with the next code, which is stored in the card for the next time, making every other copy (possibly including the original) unusable. If the card emulator doesn't store the rolling code, you are completely locked out.

Some cards have a proper challenge-response mechanism that works and can't be easily copied.