Contactless bank cards setting off the security alarms in shops

Posted 27th Jun 2019
It started a few months ago where every now and again the alarm would go off when I entered and exited the store. Not every store and not every time. I definitely remember it happening in Asda, Lidl and B&Q.

After a while I realised it was the credit and debit cards in my wallet that were setting the alarms off.

I have quite a collection (mainly from unused credit card accounts where I have shifted the balance around) and it seems that if you stack enough contactless cards together the signal is strong enough to trigger the security alarm!

It first dawned on me what was happening as I was leaving B&Q one time. I tested it by taking out my wallet and holding it up to the barrier thing and sure enough the alarm triggered. I took out a bunch of cards and held them up one by one and nothing, no alarm. But when I grouped a bunch of them together that's when the alarm went off.

So there you go. Contactless bank cards are capable of setting off security alarms.

You may have already been aware of that but it was a revelation to me, and a relief because it did cause one or two awkward moments where I had to convince the security guard I wasn't a tea leaf!
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  1. deleted902139's avatar
    So after explaining that to them you got away with the bottles of Whiskey stashed under your coat ? .
  2. summerof76's avatar
    This happened to me in Lidi twice and once in Tesco. Bought a RFID purse which blocks the signal to my cards
  3. mtsk's avatar
    I call nonsense. If that would be the case million of people would have the same problem
    Nicmann's avatar
    Old post I know, but yes your contactless cards all use radio frequencies to communicate with the card machines, some of the alarm systems operate on similar frequencies and so in some stores you might have a card that sets off the alarm system.
  4. nopartylikeansclubparty's avatar
    deleted90213927/06/2019 15:35

    So after explaining that to them you got away with the …So after explaining that to them you got away with the bottles of Whiskey stashed under your coat ? .


    They sell whisky at b&q now?
    No wonder it's packed at weekends!
    summerof76's avatar
    Went to B&Q for a saw and came out half-cut
    51672806-fnIAP.jpg
    (edited)
  5. deleted80858's avatar
    summerof7627/06/2019 16:49

    This happened to me in Lidi twice and once in Tesco. Bought a RFID purse …This happened to me in Lidi twice and once in Tesco. Bought a RFID purse which blocks the signal to my cards


    Why so many credit cards? I thought you were wadded
  6. youldyboy's avatar
    Witnessed it happen to a woman entering House of Fraser she said the same thing about it being her contactless card, I thought she was full of BS ...... You live you learn
  7. deleted17812's avatar
    summerof7627/06/2019 16:49

    This happened to me in Lidi twice and once in Tesco. Bought a RFID purse …This happened to me in Lidi twice and once in Tesco. Bought a RFID purse which blocks the signal to my cards



    deleted8085827/06/2019 19:27

    Why so many credit cards? I thought you were wadded



    "Stacked" was the preferred term.
  8. Pandamansays's avatar
    My library books trigger the alarms too
  9. Freddy_uk's avatar
    I had an old wallet that did this so occasionally held it above my head to stop it being detected
  10. deleted1863989's avatar
    Why do people say "tea leaf'
  11. deleted1863989's avatar
    jaketheplumber28/06/2019 19:15

    Cockney rhyming slang for thief I think.


    Londoners are so weird they have to associate even robbers with tea

    If I was a police officer and someone said "oi copper some bloody *anker tea leaf stole ma bike" I would laugh (edited)
  12. mysmugcat's avatar
    Great thread and comments
  13. landros1's avatar
    summerof7627/06/2019 16:49

    This happened to me in Lidi twice and once in Tesco. Bought a RFID purse …This happened to me in Lidi twice and once in Tesco. Bought a RFID purse which blocks the signal to my cards


    I had the same problem but an RFID proof wallet cured their problem.
  14. mrtickle666's avatar
    It’s the magnetic strips not the contactless apparently. I spoke to a guard after numerous times of setting alarms off. I suggest putting you cards so the strips on the back are all in different places. Eg 1 upside down, 1 back to front. Worked for me
    Nicmann's avatar
    It’s not the magnetic strips, it’s the contactless element of your card. All work on different frequencies and if it’s the same as the freq of the alarm system it will go off. All of your cards put out low power signals when close to an activating device, usually the card reader often the alarm system!
  15. deleted1471098's avatar
    It’s not a problem if you have an RFID wallet which blocks it.
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