# Tips on magnetizing a demagnetized card when rent is due and the bank is closed **URL:** \ **Category:** Factual Questions\ **Created:** [January 4, 2004, 12:23am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550 "2004-01-04T00:23:24Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![cathee](https://avatars.discourse-cdn.com/v4/letter/c/bbe5ce/32.png) [@cathee](https://boards.straightdope.com/u/cathee)\ **Post date:** [January 4, 2004, 2:36am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/21 "2004-01-04T02:36:06Z")
Baraqiyal-invaluable tip! First market I called said yes, and I didn’t even have to cross a picket line (Stater Bros) =\> I’m off to get my cash back and take care of everything. Talk about Happy New Years after all and the Straight Dope community saved the day and conquered yet some more ignorance! HoooRAaayy! ---
**Author:** ![Baraqiyal](https://avatars.discourse-cdn.com/v4/letter/b/ecccb3/32.png) [@Baraqiyal](https://boards.straightdope.com/u/Baraqiyal)\ **Post date:** [January 4, 2004, 2:43am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/22 "2004-01-04T02:43:55Z")
Great news! ---
**Author:** ![aaelghat](https://avatars.discourse-cdn.com/v4/letter/a/c5a1d2/32.png) [@aaelghat](https://boards.straightdope.com/u/aaelghat)\ **Post date:** [January 4, 2004, 2:51am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/23 "2004-01-04T02:51:50Z")
I’m happy your situation is resolved. One thing to note is that the magnet in your wallet probably did not demagnetize your card. Mythbusters recently did an episode on this, and standard magnets just don’t have enough magnetic force to demagenetize ATM or credit cards. They also debunked the eelskin wallet myth in the same episode. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 4, 2004, 3:05am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/24 "2004-01-04T03:05:40Z")
> [@](#): > > \*Originally posted by aaelghat \* > **One thing to note is that the magnet in your wallet probably did not demagnetize your card.** I wouldn’t bet on it: > [@](#): > > Erasure Resistance: > The ability of a magnetic stripe to resist a signal loss of \>15% when brought into intimate contact with a magnetic field. Resistance to a flux of 2000 gauss, for instance, would provide reasonable expectancy of survival in a household environment. See SFD, Coercivity. > [@](#): > > Commercially available neodymium-based magnets are NdFeB (Neodymium-Iron- Boron). Their remanence is generally in the range of 10,500-14,000 Gauss. For comparison, SmCo (Samarium-Cobalt) runs in the 8,000-12,000 Gauss range, Ferrite (the most widely used material) is 2,000-4,000 Gauss, and Alnico (Aluminum-Nickel-Cobalt) comes in a huge variety of alloys that span 6,000-13,500 Gauss. The earth’s magnetic field is about 0.1 Gauss at the surface. From [here](http://www.aimglobal.org/technologies/card/msglossary.htm) and [here](http://www.madsci.org/posts/archives/may98/893685016.Ph.r.html), respectively ---
**Author:** ![cathee](https://avatars.discourse-cdn.com/v4/letter/c/bbe5ce/32.png) [@cathee](https://boards.straightdope.com/u/cathee)\ **Post date:** [January 4, 2004, 3:20am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/25 "2004-01-04T03:20:12Z")
Baraqiyal-invaluable tip! First market I called said yes, and I didn’t even have to cross a picket line (Stater Bros) =\> I’m off to get my cash back and take care of everything. Talk about Happy New Years after all and the Straight Dope community saved the day and conquered yet some more ignorance! HoooRAaayy! ---
**Author:** ![cathee](https://avatars.discourse-cdn.com/v4/letter/c/bbe5ce/32.png) [@cathee](https://boards.straightdope.com/u/cathee)\ **Post date:** [January 4, 2004, 3:29am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/26 "2004-01-04T03:29:57Z")
wow, how did that happen…possible site bug to check for guys… anyhoo aaelghat–i’m going to have to disagree with you and Mythbusters…refer to the article on eelskin here on straight dope [http://www.straightdope.com/classics/a3\_388.html](http://www.straightdope.com/classics/a3_388.html) on new years eve i used my card around 5pm, went home and transferred my stuff to a brand new leather purse along with 2 blinking magnetized “2004” trinkets for later that eve. the diameter of the magnets were that of a watch battery. I have no doubt that is what did it…I still recommend not putting magnets anywhere near your cards because it isn’t worth the stress. or thank god stater bros is open til 10 and experiment for yourself. oxo ---
**Author:** ![aaelghat](https://avatars.discourse-cdn.com/v4/letter/a/c5a1d2/32.png) [@aaelghat](https://boards.straightdope.com/u/aaelghat)\ **Post date:** [January 4, 2004, 4:00am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/27 "2004-01-04T04:00:30Z")
**QED** I don’t dispute the authenticity of your cites, but the second cite refers to extremely powerful, specially made commercial magnets. Refrigerator magnets in contrast are only about 10 gauss ([cite](http://www.serenity2000.com/aboutgauss.html)). I’d be hard pressed to believe what was in cathee’s purse exceeded 100 or 200 gauss at most. In the particular episode of the Mythbusters I mentioned before, they performed an experiment where they encoded 50 or so “credit cards” and subjected them to ever-increasing magnetic fields from an electromagnet, recording the point at which there was data loss. I can’t remember how many gauss it took for data loss to happen, but it was very high - (over 1,000 gauss). They also took a magnetic money clip and subjected credit cards to the magnetic field from that and didn’t see any noticeable effect. The interesting thing here is that cathee’s link from Cecil disputes the conclusions of the experiment performed in the paragraph above. However, Jamie Hyneman and Adam Savage (the folks on the Discovery Channel program) conducted the closest thing I’ve ever seen to a controlled experiment. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [January 4, 2004, 4:10am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/28 "2004-01-04T04:10:43Z")
No, a refrigerator magnet is closer to [1000 gauss](http://education.magnet.fsu.edu/maglabalpha/html/expeditions/viewingfield.html). The reason those flexible types feel so weak is that they are actually magnetized in parallel trips of opposing polarity. Close to the surface of the magnet, the field is quite strong, because each stripe’s field is isolated from the others at small distances. But a very small distance away from the surface, the approximately equal, but opposite, magnetic fields begin to cancel one another out. On the other hand, it’s not terribly difficult to find much stronger magnets. I have several from various sources \> 5 kilogauss. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 4, 2004, 5:34am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/29 "2004-01-04T05:34:18Z")
> [@](#): > > \*Originally posted by aaelghat \* > \*\*They also took a magnetic money clip and subjected credit cards to the magnetic field from that and didn’t see any noticeable effect. > > The interesting thing here is that cathee’s link from Cecil disputes the conclusions of the experiment performed in the paragraph above. However, Jamie Hyneman and Adam Savage (the folks on the Discovery Channel program) conducted the closest thing I’ve ever seen to a controlled experiment. \*\* I can assure you that a magnetic money clip messed up a card for me. Seeing that cathee, Cecil, and I have had experiences that contradict the results you’ve reported, I would venture that the most likely explanation is that the experiment was flawed in some way. ---
**Author:** ![voltaire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/voltaire/32/313_2.png) [@voltaire](https://boards.straightdope.com/u/voltaire)\ **Post date:** [January 4, 2004, 6:02am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/30 "2004-01-04T06:02:43Z")
A flawed experiment on Myth Busters?! Inconceivable! (we need a “tongue in cheek” smiley) I would guess that the “flaw” was that they didn’t try it with a wide variety of mag-stripe readers and encoders. A better experiment would have had a variety of cards encoded by different encoders being tested through a variety of mag-stripe readers. ---
**Author:** ![aaelghat](https://avatars.discourse-cdn.com/v4/letter/a/c5a1d2/32.png) [@aaelghat](https://boards.straightdope.com/u/aaelghat)\ **Post date:** [January 4, 2004, 6:20am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/31 "2004-01-04T06:20:14Z")
OK, I’ll subscribe to the fact that there’s a wide variety of cards and encoders that MythBusters didn’t test. After doing some more web research I found this: > [@](#): > > Magstripes themselves come in different flavors. The COERCIVITY of the > magnetic media must be specified. The coercivity is the magnetic field > strength required to demagnetize an encoded stripe, and therefore determines > the encode head field strength required to encode the stripe. A range of media > coercivities are available ranging from 300 Oersteds to 4,000 Oe. That boils > down to HIGH-ENERGY magstripes (4,000 Oe) and LOW-ENERGY magstripes (300 Oe). > > REMEMBER: since all magstripes have the same magnetic remanence regardless of > their coercivity, readers CANNOT tell the difference between HIGH and LOW > energy stripes. Both are read the same by the same machines. > > LOW-ENERGY media is most common. It is used on all financial cards, but its > disadvantage is that it is subject to accidental demagnetization from contact > with common magnets (refrigerator, TV magnetic fields, etc.). But these cards > are kept safe in wallets and purses most of the time. > > HIGH-ENERGY media is used for ID Badges and access control cards, which are > commonly used in ‘hostile’ environments (worn on uniform, used in stockrooms). > Normal magnets will not affect these cards, and low-energy encoders cannot > write to them. I found that snippet here: ---
**Author:** ![cathee](https://avatars.discourse-cdn.com/v4/letter/c/bbe5ce/32.png) [@cathee](https://boards.straightdope.com/u/cathee)\ **Post date:** [January 4, 2004, 6:40am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/32 "2004-01-04T06:40:23Z")
awsome link aaelghat. ---
**Author:** ![cathee](https://avatars.discourse-cdn.com/v4/letter/c/bbe5ce/32.png) [@cathee](https://boards.straightdope.com/u/cathee)\ **Post date:** [January 4, 2004, 6:48am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/33 "2004-01-04T06:48:55Z")
awsome link aaelghat. ---
**Author:** ![Iteki](https://avatars.discourse-cdn.com/v4/letter/i/eada6e/32.png) [@Iteki](https://boards.straightdope.com/u/Iteki)\ **Post date:** [January 4, 2004, 11:11am UTC](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550/34 "2004-01-04T11:11:24Z")
Glad things worked out for you! While we are on the topic of old-wives-tales and shots in the dark, I can reccommend the following method, it has worked before, but now that I think of it it may just have been cleaning the strip more than anything else. Anyhoo, what sometimes helps is to take the card and rub it on your leg. I don’t know if it “works” on other trousies than jeans. You want to use long strokes in only one direction (obviously against the lenght of the card). Couple of firm strokes (:eek:) has worked for me before. [Previous page](https://boards.straightdope.com/t/tips-on-magnetizing-a-demagnetized-card-when-rent-is-due-and-the-bank-is-closed/222550.md?page=1)