The Security Card is a black plastic card used to double check transactions as a second factor of authentication. The security card is only required with the Nano or the HW.1 devices as they don't have any screen to check directly the integrity of transactions.
- If you own a Nano S or a Blue, you can't and don't need to use such a card, because the authentication process is yet included by design in your device. Your device features its own screen which displays an authentication push for each transaction, requiring your manual consent to sign it.
- If you own a Nano or a HW.1, this card is provided with your device in your box. You will be asked to take it for each sending transaction from your Chrome application.
When you click on "Send" after having filled the amount and recipient address, the Bitcoin Chrome app asks you to choose between 2 ways of validation: Ledger Authenticator or Security Card. Both are made to authenticate your transaction, but with different methods.
The Security Card is a physical way to find 4 corresponding digits by matching lower cases, upper cases and numbers following the displayed instructions.
If you lost your Security card, you can print a new copy or generate a new one.
Ledger Authenticator is a mobile application made to replace the Security Card if you prefer using a smartphone. This application will display a code each time you want to verify your transaction. You can know more about it here.