There is a sentinel character on the mag stripe which identifies the card as chip and pin. As mentioned in the README of this repo, it can be disabled - for the

There is a sentinel character on the mag stripe which identifies the card as chip and pin. As mentioned in the README of this repo, it can be disabled - for the purposes of backwards compatibility, this is a necessary evil. Fortunately, it is easy to detect! The terminal will send the magstripe data online when authorizing the transaction, and the backend systems will identify the corruption in magstripe data and identify it as fraud.