There’s a process to it. Every card, as part of the mag-stripe, has a little bit of data on it called the Service Code. It’s three characters. Part of that tel

There’s a process to it. Every card, as part of the mag-stripe, has a little bit of data on it called the Service Code. It’s three characters. Part of that tells the terminal if the card has an EMV chip. The terminal is required (I believe, by the brands) to force you to use the chip. The chip has to fail a set number of times (I believe usually 3) before it will process a mag-stripe transaction. Even then, the payment processor is informed this transaction was a failed chip transaction that fell back to msg-stripe. So the processor can determine if they want to take the risk. (Of course this doesn’t apply to mag-stripe only devices like older gas pumps)