# BART tickets, cell phones, and magnets **URL:** \ **Category:** Factual Questions\ **Created:** [September 23, 2007, 1:14pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191 "2007-09-23T13:14:08Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![zuma](https://avatars.discourse-cdn.com/v4/letter/z/e9c0ed/32.png) [@zuma](https://boards.straightdope.com/u/zuma)\ **Post date:** [September 23, 2007, 1:14pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/1 "2007-09-23T13:14:08Z")
Last night I saw a sign on the bart (bay area rapid transit… SF bay area mass transit train type thing) ticket machine (you put money into a machine, and it spits out a ticket) that said something close to this: “Do not place your bart ticket next to magnets or cell phones. They may erase your ticket” I think this was at the Powell station, but it may have been embarcadaro or montgonmery. This seems like total bullshit. We went over this with the eel skin wallet, didn’t we? A bart ticket is a paper credit-card sized thing with a magnetic strip that looks like this: [http://content.answers.com/main/content/wp/en/thumb/a/ae/180px-BART\_ticket.png](http://content.answers.com/main/content/wp/en/thumb/a/ae/180px-BART_ticket.png) This has to be crap right… We went over this magnetic strip thing a long time ago?? These magnetic strips on the paper ticket have been in use for at least 30 years, probably 40. ---
**Author:** ![audiobottle](https://avatars.discourse-cdn.com/v4/letter/a/bc8723/32.png) [@audiobottle](https://boards.straightdope.com/u/audiobottle)\ **Post date:** [September 23, 2007, 1:26pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/2 "2007-09-23T13:26:42Z")
I’m not sure if it’s legitimate, but I do know a guy in front of me at the DC Metro office was asking what erased his card. The Metro worker asked if he had kept it by his cell phone, the guy said yes, and the Metro worker told him that’s probably what erased it. So even if it’s not true, people all over believe it. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [September 23, 2007, 3:08pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/3 "2007-09-23T15:08:51Z")
I haver not conducted a scientific test of this but certainly my experience is that your cell phone can indeed erase these cards. On numerous occasions I have kept my cellphone in my shirt pocket as well as putting the paper card from a parking machine (complete with magnetic strip) there as well. Many times upon returning to the garage my parking ticket was deemed unreadable by the machine and I had to go to the garage office and have them manually check me out. Of course the first few times this happened I just figured I had a bad card and did not think much of it but it happened often enough that I made the connection. As soon as I had the two stop sharing the same pocket I never had a problem. ---
**Author:** ![mks57](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@mks57](https://boards.straightdope.com/u/mks57)\ **Post date:** [September 23, 2007, 3:23pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/4 "2007-09-23T15:23:56Z")
Your cell phone has permanent magnets and electromagnets inside it. Why do you think it’s bullshit? The coercivity of the magnetic strip determines how difficult it is to erase it. They may have chosen a low coercivity (easy to erase) recording media for reasons of cost. ---
**Author:** ![JayRx1981](https://avatars.discourse-cdn.com/v4/letter/j/71e660/32.png) [@JayRx1981](https://boards.straightdope.com/u/JayRx1981)\ **Post date:** [September 23, 2007, 3:42pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/5 "2007-09-23T15:42:20Z")
This actually happened to me when I was visiting San Fran back in June. I put my Bart ticket in my pocket with my cell phone when we got off the Bart train earlier in the day and by the time we were ready to hop on to the next one later on, it didn’t work anymore. So yeah, its true, at least as far as I’ve experienced. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [September 23, 2007, 3:50pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/6 "2007-09-23T15:50:36Z")
I think it’s possible, but unlikely. All of the anecdotes above do not rise to the level of scientific proof. ---
**Author:** ![FatBaldGuy](https://avatars.discourse-cdn.com/v4/letter/f/ecd19e/32.png) [@FatBaldGuy](https://boards.straightdope.com/u/FatBaldGuy)\ **Post date:** [September 23, 2007, 4:06pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/7 "2007-09-23T16:06:17Z")
There was a story in the news a few weeks ago about certain Nissan keys with embedded computer chips being erased by cell phones kept in the same pocket. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [September 23, 2007, 4:16pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/8 "2007-09-23T16:16:10Z")
[QUOTE=zuma] Last night I saw a sign on the bart (bay area rapid transit… SF bay area mass transit train type thing) ticket machine (you put money into a machine, and it spits out a ticket) that said something close to this: “Do not place your bart ticket next to magnets or cell phones. They may erase your ticket” … This seems like total bullshit. We went over this with the eel skin wallet, didn’t we? [/QUOTE] We did, but I don’t think Cecil’s [column on eelskin wallets](http://www.straightdope.com/classics/a3_388.html) supports your position: > [@Cecil Adams](#): > > After a sudden rash of complaints about bad cards from eelskin-wallet owners, Katie and her colleagues examined the magnetic stripe on several failed cards and found that magnetic information had in fact been erased. They further noted that most of the complainers were women who used eelskin wallets with large magnetic clasps. As an experiment, Katie ran a variety of magnetic items over some test cards. Sometimes the cards became demagnetized, sometimes not. But when she ran an eelskin-wallet clasp over the cards, they always became demagnetized, even at a distance of two inches. It seems pretty clear from this that magnets can erase magnetic strips. ---
**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\ **Post date:** [September 23, 2007, 5:34pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/9 "2007-09-23T17:34:53Z")
> [@](#): > > These magnetic strips on the paper ticket have been in use for at least 30 years, probably 40. Yeah, but cell phones haven’t. Unfortunately, cursory googling to dig up figures on the strength of the magnetic field produced by cell phones brings up a lot of scare stuff about health issues. Which is very likely BS. It’s not unlikely that the phone could wipe something like a BART or parking lot ticket, though, if you happen to put the thing right next to the phone, which is also not unlikely. I suspect that encoding a mag strip onto a thin flexible substrate on paper forces you to make it with a pretty low coercivity, as referred to by **mks57** , apart from just cost issues. This blurb about particular cell phone model is interesting: > **[Sidekick 3 Warning: Sidekick 3's Magnet Will Erase Your Credit Card in Under...](http://www.theinternetpatrol.com/sidekick-3-warning-sidekick-3s-magnet-will-erase-your-credit-card-in-under-a-second/)** > > The Sidekick 3's swivel screen is held in place by a magnet. An incredibly strong magnet. In fact, it turns out, a magnet strong enough to wipe all your credit card or other magnetic strip card data in under a second. Don't believe it? We have the... ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [September 23, 2007, 6:42pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/10 "2007-09-23T18:42:47Z")
Once again, I doubt it it’s the Cell Phone per se, but more likely a cell phone case with a strong magnetic catch. I’ve never seen a cell phone with a perceptible external magnetic field. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [September 23, 2007, 8:23pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/11 "2007-09-23T20:23:07Z")
[QUOTE=beowulff] I’ve never seen a cell phone with a perceptible external magnetic field. [/QUOTE] I use a Motorola RAZR and it has had paper clips stick to the bottom edge (via magnetism). I grant my experience is not scientific but it is highly suggestive to me. I have used the same parking garage many times and the only times I had trouble with the ticket was when it shared a pocket with my cell phone for several hours. It was in my shirt pocket so the card and phone were pressed together (not like in a purse where they may be separated by some small amount). ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [September 23, 2007, 8:27pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/12 "2007-09-23T20:27:28Z")
[QUOTE=Whack-a-Mole] I use a Motorola RAZR and it has had paper clips stick to the bottom edge (via magnetism). I grant my experience is not scientific but it is highly suggestive to me. I have used the same parking garage many times and the only times I had trouble with the ticket was when it shared a pocket with my cell phone for several hours. It was in my shirt pocket so the card and phone were pressed together (not like in a purse where they may be separated by some small amount). [/QUOTE] Well, that might do it… ---
**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:** [September 23, 2007, 8:43pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/13 "2007-09-23T20:43:32Z")
Mine, too, can pick up paper clips (Samsung X-495.) It appears to be a speaker magnet, since the clips stick to the case just on the opposite side from the earpiece holes. [Photo](http://img230.imageshack.us/my.php?image=phonemagnetel9.jpg). ---
**Author:** ![counsel\_wolf](https://avatars.discourse-cdn.com/v4/letter/c/65b543/32.png) [@counsel\_wolf](https://boards.straightdope.com/u/counsel_wolf)\ **Post date:** [September 23, 2007, 8:50pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/14 "2007-09-23T20:50:05Z")
[QUOTE=mks57] Your cell phone has permanent magnets and electromagnets inside it. Why do you think it’s bullshit? The coercivity of the magnetic strip determines how difficult it is to erase it. They may have chosen a low coercivity (easy to erase) recording media for reasons of cost. [/QUOTE] This is the case. The harder you want to make a card to erase the more effort you have to put into writing to it in the first place. If you want the card to be writable by cheap (and portable) devices and to keep costs down you will often use a lo-co card as opposed to a hi-co card. Normally you can tell the difference by stripe colour (although this may be a convention rather than for physical reasons). Very dark brown stripe = hi-co (credit cards and other write once read often cards will normally be like this) light brown stripes = lo-co often appear on disposable paper tickets and on hotel keys (which need to be erased and re-written very frequently). I’m not sure about what exactly the power requirements for a hi-co printer are but last time I was setting a bank of them up putting more than one per power strip was not recommended as there was a big power spike during the encoding cycle. Summary: I wouldn’t be at all suprised if lo-co cards were interfered with by everyday environmental sources of e-mag fields but would be suprised if credit cards etc were affected. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [September 24, 2007, 4:07pm UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/15 "2007-09-24T16:07:01Z")
Another angle - what’s the relative durability of low-co vs high-co equipment? A bank card encoder has a pretty cushy life compared to that of mass transit fareboxes. The fareboxes, (actually, they’re automated gates) have to put up with a lot of abuse - every time the fares go up, people get mean for a while. I was chatting with one of their techs a while ago, and he let on that the equipment gets gunked up with a variety of body fluids that really shouldn’t be on a train ticket. (ugh!) Back to the stripes - I’ve got two BART tickets in my wallet, and they’ve got pretty dark stripes. Not as dark as the almost black ones on my bank cards, but definitely a lot darker than the milk-chocolate, nearly tan, stuff that most cheap reel-to-reel tape was. In the end, I’m sure it comes down to price - BART can’t even be bothered to print the $45 and $60 tickets on plastic stock, so forgetting to check your pockets before doing laundry can be very expensive as the paper tickets will disintegrate. Ironically, if you walk up to a ticket vending machine and buy a $2 ticket, it will be on plastic stock. ---
**Author:** ![iamthewalrus\_3](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@iamthewalrus\_3](https://boards.straightdope.com/u/iamthewalrus_3)\ **Post date:** [September 25, 2007, 1:20am UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/16 "2007-09-25T01:20:51Z")
[QUOTE=Q.E.D.] Mine, too, can pick up paper clips (Samsung X-495.) It appears to be a speaker magnet, since the clips stick to the case just on the opposite side from the earpiece holes. [Photo](http://img230.imageshack.us/my.php?image=phonemagnetel9.jpg). [/QUOTE] I confirm that this works with my Samsung something-or-other as well. ---
**Author:** ![Critical1](https://avatars.discourse-cdn.com/v4/letter/c/3e96dc/32.png) [@Critical1](https://boards.straightdope.com/u/Critical1)\ **Post date:** [September 25, 2007, 5:28am UTC](https://boards.straightdope.com/t/bart-tickets-cell-phones-and-magnets/420191/17 "2007-09-25T05:28:44Z")
A strong magnet will easily wipe a card, Mythbusters even confirmed the myth but had to tack it on to the show as an after thought kind of deal because the magnets that DID wipe cards were impossible to get an accurate reading from. [http://www.kjmagnetics.com/proddetail.asp?prod=ZDX8C-N40](http://www.kjmagnetics.com/proddetail.asp?prod=ZDX8C%2DN40) try one of those on your wallet, or hard drive, or floppy or whatever magnetic storage medium you want, I will be impressed as hell if it still has anything useful on it. cell phones regularly use Neomags for the vibration mode and if you get close those suckers will eat cards like nothing. I have close to 200$ worth of the things in various forms and they have eaten a couple cards I was careless with. (and yes they are serious with the warnings, those magnets are friggin powerful as hell, I only have one thats likely to cause any serious damage but even the little ones hurt like hell if they get a bit of skin when they come together.)