It works only within about an inch and hands over a one-time code, not your card number. A reader in somebody's pocket cannot quietly charge you in a crowd.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a handshake so brief it needs no words.
For example
You hold the card near the machine and it beeps. Somebody with a reader in their pocket cannot do that to you in a crowd — it only works almost touching.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.