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