reclusive46

Hi,
the last few times I've flown back from the US, I've been told to keep my wallet in my hand while going through a millimetre body scanner. Wouldn't this harm the magnetic stripes or chips on credit cards and IDs? Or do millimetre scanners not cause harm to magnetic data.

AllieKat

The signal strength of the millimetre wave scanner is not even remotely strong enough to affect the chips. Not even on the same planet as strong enough, being many times weaker than a mobile phone.

The magnetic stripe is an interesting question. As the scanner rotates, it has motors. There is some magnetic field. It'd never kill a high coercivity card, but I could see it killing a low coercivity card (think a paper Tube ticket) with repeated exposures. This would also apply to X-ray machines and metal detectors - magnetic fields abound at airport security.

reclusive46

Thats a good point, I never thought about the motor magnetic field. So in summary, the millimetre waves wouldn't affect the Magnetic Stripe or Chip as they are basically the same as radio waves but the magnetic field could possible erasure low strength stripes like some Loyalty cards or parking tickets but never things like credit cards or IDs?

AllieKat

Yup, exactly.

gobluetwo

For what it's worth, the dozens of trips through security i've taken have not affected any of my "low coercivity cards" (I'm thinking my Oyster card, MTA card, CTA card, etc.), despite "repeated exposures." Not something I'd worry about.

AllieKat

Your Oyster card is a contactless smart card, definitely not something that could be affected.

I don't know what the MTA and CTA cards are but if they're permanent, they're PROBABLY hi-co, as a Reclusive's loyalty cards, but I don't have them in front of me so I can't prove that

Lo-co cards are light brown and usually used for paper tickets and cards that will be rewritten often, like hotel room keys.

gobluetwo

Maybe an old Oyster card, but CTA and MTA are the Chicago and NYC subway systems and I'm referring to the paper cards (ok, the paper CTA card is a Ventra card now, but same diff). Still would consider magnetic fields from these machines erasing the data on these cards a practical non-concern.

AllieKat

Oyster has always been a contactless smartcard system. You may be thinking of pre-Oyster paper tickets (which you can still get for some bizarre reason, Oyster is a much better value...)

I knew what CTA and MTA were, just not the cards. If they're paper then yes, they're probably low coercivity, and prone to magnetic field damage. One exposure to airport security equipment? Not a likely concern, no. But repeated exposures and bad luck? Yes.

Note, purse closures (magnetic ones) and other low intensity magnetic fields all damage these cards, so it's not an airport security concern. Low coercivity cards are designed to have a short lifetime. Though, when you need a new hotel key every night, it is too short...

WillCAD

It takes a pretty strong magnetic field to damage credit and debit card magnetic strips without physical contact. If the magnetic field generated by a MMW scanner isn't strong enough to make nearby metal objects stick to it, then it's most definitely not strong enough to damage the mag strip on a card, not even with repeated exposure.

The most common source of magnetic strip failure is not magnetic fields, or even static electricity (though static is a genuine danger), it's physical damage, i.e. scratching, caused by sliding the card in and out of wallets and through card readers on a daily basis.

AllieKat

I was thinking more hotel keys/paper tickets/etc. They're already low-coercivity devices and are likely to be demagnetised with REPEAT exposures to many fields in your daily life.

WillCAD

Even so, static and scratches are far, far more likely to cause a malfunction than a magnetic field.

The whole term "demagnetized" is a misnomer. Strong - and I mean POWERFUL - magnetic fields can scramble the information in a magnetic strip, but the strip doesn't actually demagnetize. It's still a magnetic strip, it's just had its encoded information scrambled. Refrigerator magnets won't do it. The magnets in your cell phone holster or purse won't do it. To scramble the information on those strips with a magnet takes a field at least as powerful as a rare earth magnet, and usually much more powerful.

So, I'm not worried a bit about my various mag strip cards being damaged by any ordinary machinery I might encounter, even the MMW scanner or the microwave oven.