The recorded information of bank cards and bankbooks are stored on the magnetic stripe on the back. The strong magnetic field generated by high-frequency electromagnetic waves generated when the mobile phone works will magnetize the credit card, making the recorded information disordered, thus leading to the invalidation of the bank card. At the same time, some people put mobile phones, bank cards and other items together in their bags, which can easily lead to the bank cards being "degaussed". In addition, if the magnetic strips of two bank cards overlap, they are likely to be demagnetized at the same time. In addition, some medical inspection equipment such as the magnetic hidden buckle of ladies' handbags, card readers on buses, nuclear magnetic resonance instruments, etc. will also cause the bank card to be magnetized.