Mifare Classic: Fully Locked Card

Mifare Classic cards are divided into sectors, with two keys for each sector which is used to access data.

These keys can sometimes be cracked.

However, Mifare Classic does not have an open "application directory" like newer Mifare (DESFire) and FeliCa cards have, which is accessible even when no keys are known.

As a result, any card which is "fully locked" (such as Go (SEQ)) will not be identified by Metrodroid until you have installed keys.

Metrodroid will show a warning when you have tapped a fully-locked card and you do not have keys installed for it.