All electronic devices radiate energy in the form of an electromagnetic field. Electromagnetic Interference (EMI) is the disruption of the normal operation of an electronic device when it is in the vicinity of an electromagnetic field created by another electronic device.
Some electrical equipment has the potential to interfere with the proper function of an implanted device i.e. ICD, pacemaker and so precautions must be taken when in or around electrical equipment.
If the device owner moves away from or turns off the source of EMI, the implanted device usually resumes its normal mode of operation.