It probably differs from issuer to issuer. In my experience Amex is very on top of it and they have always flagged every transaction I have not made myself, imm

It probably differs from issuer to issuer. In my experience Amex is very on top of it and they have always flagged every transaction I have not made myself, immediately sending push notification and SMS where I can ack/nak an automated transaction prompt. If I nak it they freeze the card and overnight a new one. I suppose they don't really care about handling it manually because that would be prohibitively expensive and they prefer to act on the patterns in an automated way. Would be interesting to see aggregate stats by card issuer of how good they are at detecting it.