This article on the demise of the magstripe https://hackaday.com/2024/08/21/farewell-magnetic-stripe/ brought some memories to me.

When I was working at a local computer shop, we'd still use a zip zap machine (a credit card imprinter). We did not have a magstripe reader.

In order to check whether a card was still valid, I had to call the acquirer and recite the card number to them over the phone. Sometimes we did that.

I would take a pile of those imprinted slips into the bank weekly and I assume they'd type the card numbers in. A customer that'd used a debit card once called in to complain that I'd taken the slip to the bank only after a couple of weeks. Their account ended up overdrawn as they had already spent the money on something else. I thought this was totally weird: how would anyone not notice that we'd not yet debited the (expensive) computer? Myself, I would not have had money to buy anything like that until years later.

Much later, I saw a sign at a local grocery store saying they don't accept Diner's Club. Of course, nobody usually accepted it anyway, but this sign said that Diners cards "break the card terminals".

Being in IT, I thought this is just some crappy (exploitable?) POS device coding, but being a Diners Club cardholder then (it was our company card) I realized Diners had recently sent me a cool new card with a silver-coloured magstripe. So I asked around.

Turns out, the silver magstripe was conductive. And the supermarket cashiers were wearing trousers made of plastic fibres, sitting on plastic chairs, on a non-conductive flooring.

They were grounding themselves to the poor POS terminal via the magstripe.