No, you can’t demagnetize a SmarTrip card…

Sometimes, a SmarTrip card will fail—either it consistently won’t work when tapped on a Metrorail faregate or Metrobus farebox, or perhaps it needs to be tapped a few times before it works. Of course, it’s frustrating when it happens—but, contrary to popular opinion, it’s not because the card is ‘demagnetized’.

SmarTrip is a contactless smart card, not a magnetic-strip card like the conventional Metrorail farecard. When we say that a magnetic-strip card (like a Metrorail farecard, or a MetroCard in New York) has been demagnetized, that actually means something—that the magnetic strip has somehow lost its encoding.

But SmarTrip isn’t a magnetic-strip card; it’s a smart card. Contactless smart cards, like SmarTrip, consist of a chip and an antenna, made of thin copper wire, running around the perimeter of the card. The chip itself is truly tiny—no more than a few millimeters on each side, and less than a millimeter thick. (You can see the innards of an Oyster card, including the chip and antenna, in this video.) There’s no magnetic strip involved, so there’s nothing to ‘demagnetize’. It’s possible for very strong electromagnetic fields (like those found in a microwave oven, or produced by a HERF gun) to destroy the chip in a SmarTrip card, but the RF intensities required are so high that if you’d been exposed to such an electromagnetic field, you’d know it. Proximity to other cards is also very unlikely to harm a contactless smart card.

So, if there’s nothing to demagnetize, then what has happened when a card fails? Even if the card isn’t externally cracked, the antenna may have broken inside the card, in which case it’ll no longer be readable. The other possibility, equally likely, is that the chip has simply failed. SmarTrip is the nation’s oldest contactless smart card for a transit system, and some of the cards in circulation now are getting very old in technological terms. Smart cards have a finite lifetime, and eventually they’ll need to be replaced.

Considering the ire of some commuters on Twitter, it also seems vital to point out that riders need not pay for a replacement SmarTrip card if it fails (and the value on the old card will be transferred to the new, replacement card). While I would prefer that the replacement be done on-the-spot (which would be the case if we had real ticket offices, like on the Tube), the point remains that riders are not responsible for paying to replace a card which has become defective.