The situation
Availability is part of security.
A secret you cannot reach is not safe, it is just unavailable. Most of the time that difference does not matter. During an outage it is the only thing that matters.
A card carries what it holds on itself. Reading it needs a phone with some charge and nothing else: no network, no account, no service that has to be running.
That does not make the card magic. It makes it independent, which is a different and more useful property.
During an outage.
Needs a network
- Online storage
- Yes, no connection, no vault.
- A card in your pocket
- No. The data is on the card.
Needs an account
- Online storage
- Yes, and account recovery needs the network too.
- A card in your pocket
- No account exists.
Depends on a company
- Online storage
- Their servers must be up.
- A card in your pocket
- Nothing to be up.
What you need
- Online storage
- Signal, power, a working service.
- A card in your pocket
- A phone with charge, and your password.
Independent beats
convenient, once.