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Mythbusters: Can a mobile phone erase a hotel key card?

It’s a warning any seasoned traveler has probably heard: Don’t carry your hotel key card in the same pocket as your cell phone or the card could get erased. Some travelers cautiously heed the advice, while others write it off as urban legend.

Even among card industry professionals, there are varying opinions on whether cell phones can actually erase or damage data from magnetic stripe cards. There is agreement, however, that there are other variables that will damage these cards.

CPI Card Group, a card manufacturer based in Littleton, Colo., believes it has evidence of the cell phone-mag stripe correlation. CPI manufacturers a mix of magnetic stripe cards, including payment cards as well as gift cards, hotel key cards and casino gaming cards. “A lot of the cards people tend to use in harsh way,” explains Julie Hermanson, quality control manager for CPI.

Cardholders typically protect their credit cards in an enclosed place such as a wallet, but hotel key cards are often carried in a person’s pocket next to their cell phone. “The mag stripe is often exposed to magnetic fields that can cause the encoding to degrade or erase,” Hermanson says.

Putting it to the test

In 2009, CPI conducted internal studies in which card users carried mag stripe movie theater cards in their pockets with a cell phone that had no magnetized case around it. After the cards were carried with the cell phone for about three hours, testers started to see the encoding on the stripes being disturbed.

I have been in this industry for 16 or 17 years, and I have yet to find an instance of a card accidentally becoming demagnetized by a source other than an actual encoder or outright magnet.

When the problem is truly with the magnetic stripe, outside interference is most often the cause. “The number one issue was cards being demagnetized by being carried next to a cell phone or set on a TV in a hotel room,” Hermanson says. “Anything with an electromagnetic field transmitting from it can cause a mag stripe to demagnetize.”

Often, however, the problem is not really with the mag stripe material. Frequently when problems are reported, it turns out that the encoding equipment needed to be cleaned or maintained, or there were lock malfunctions at the hotel, Hermanson says.

Another industry veteran, however, isn’t buying it. Shane Cunningham, marketing and communications manager for card printer manufacturer Digital Identification Solutions, believes the idea of a cell phone erasing a magnetic stripe card is bogus.

“I have been in this industry for 16 or 17 years, and I have yet to find an instance of a card accidentally becoming demagnetized by a source other than an actual encoder or an outright magnet,” he says.

Cunningham expressed doubts even after seeing the CPI study, pointing out that the test utilized cards at the bottom of the coercivity spectrum, meaning the cards most easily erased or damaged.

Cunningham travels about 12 weeks of the year for work and frequently comes into contact with hotel key cards. In his own travel experience, he has seen hotels propagate the cell phone-key card theory.

After receiving two room cards and checking both to make sure they worked, he put one in his wallet next to his credit card. He left the other in a shielded sleeve in his room.

The next night, the key in his wallet still worked. On his third night, which was an extended stay, neither card would open his door. “The first words out of the mouth of the person at the desk were, ‘Did you have it in your wallet with your cell phone?’”

“I can almost guarantee you that when I booked my room, they didn’t book my third night. So when I went up that night, the key cards didn’t work,” he says. “But the first thing that came to (the attendant’s) mind was that I must have somehow erased them.”

Mag stripe enemies

Cell phone debate aside, industry experts point to a number of other reasons why mag-stripe cards fail. The more likely culprit in the mag stripe card mystery is the quality and age of the card itself or the equipment used to encode and read the card, Cunningham explains. “My personal opinion is that these cards used by hotels aren’t designed to be coded and re-encoded multiple times,” he says.

That means that if hotels program and deprogram cards to open a different room every few nights, eventually the cards’ mag stripes are simply going to wear out.

Hotels typically use low-cost encoders, Cunningham says, so the data can become garbled. Unlike credit card companies, hotels tend to order cheaper, lower quality cards to keep their costs down.

Mag stripes vary in coercivity, the measure of how difficult it is to encode and thus erase information from the magnetic stripe. Coercivity of about 300 Oersteds (Oe) is considered to be low coercivity (LocCo) and is primarily used for short-term use cards and those where data may be changed, such as hotel key cards. Most credit cards use magnetic stripes with at least 2,750 Oe that are considered high coercivity (HiCo).

The first words out of the mouth of the person at the desk were, ‘Did you have the card in your wallet with your cell phone?’

Low coercivity cards are fairly easy to encode, but they also tend to be more susceptible to accidental erasure and damage, Hermanson says. They are also less expensive.

“Hotel cards are a commodity-driven product, so price is very important. LoCo mag stripes are cheaper than HiCo, so it’s difficult to make that switch,” Hermanson says.

But even HiCo cards can erase if exposed to strong enough magnets. Also, if mag stripes are scratched across the surface of the stripe, they can cause swipe readers to skip, she says.

Myth two: credit cards demagnetizing hotel key cards

When Cunningham’s key cards ceased to work and he told the hotel attendant that he did not have the card next to his cell phone, the attendant asked whether he had the card in his wallet next to his credit cards. This highlights another common question relating to magnetic stripe damage. Can a HiCo card, such as a credit card, demagnetize a LoCo hotel key card?

Both Cunningham and Hermanson say no. Despite what you may hear in the hotel lobby, it is not unsafe to store two cards with their mag stripes facing each other. “I have not been able to reproduce actual degradation of the encoding by having the cards together,” Hermanson says.

Carrying a key card next to other credit cards could damage the mag stripe but only because the raised numbers on the credit card could scratch against and damage the key card’s stripe, Cunningham says.

The mag stripe’s future

As smart cards gain prominence in the market, the debate over whether cell phones affect mag stripe cards could become moot. “I’m pretty sure in the next five years, you won’t see mag stripe cards anymore,” Cunningham says.

In Digital Identification Solutions’ European offices, he explains, magnetic stripe cards are hardly ever used because everything is switching to contact and contactless chip cards.

But mag stripe cards remain king in the U.S. because of the massive infrastructure in place to support them. Mag stripe material overall is extremely robust, Hermanson says, adding that the handful of manufacturers adhere to very strict standards.

“A mag stripe can hold a tremendous amount of information in a fairly secure manner, and for a relatively low cost. And I think those remain its major advantages,” she says.



Mag stripes put to the test

In 2009, CPI Card Group conducted a series of durability tests on sample theater cards with low-coercivity magnetic stripes of 300 Oersteds. The issued cards were returned with evidence of what appeared to be partial erasure. The cards were issued to theater patrons. They used the card at the concession stand at least once but found it was unreadable when they tried to use it again later.

Carried in a Blackberry holster for 15 minutes.No disturbance of encoded mag stripe tracks.
Carried in a Blackberry holster for 30 minutes.Disturbance was visible on the right edge of encoded tracks similar to field failures.
Carried in a Blackberry holster for 45 minutes.Some possible degradation of one of the mag stripe’s three tracks but only minor disturbance of encoded tracks; card still read back.
Carried in a Blackberry holster for 1 hour.No disturbance of encoded tracks.
Randomly rubbed a kitchen magnet across encoded tracks.Disturbance of encoded tracks that followed the pattern of the rub; not similar to field failure.
Control card encoded not exposed to magnetic field.No disturbance of encoded tracks.
Placed a high-strength magnetic badge holder on top of card.Disturbance across encoded tracks similar to field failures – significant bar pattern noticeable. Testers suspect this was due to the higher strength magnet.
Attached the card to a magnetic white board with a common kitchen magnet.Data was wiped out in the area of the magnet.
Carried in a Blackberry holster overnight.Disturbance across encoded tracks similar to field failures.
Affixed a common kitchen magnet to front and back of the card.Data wiped out in area of the magnet.

Source: CPI Card Group

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