In the technical field of known cardholders for devices such as cards with magnetic stripes on which is encoded informa- tion and/or data in the form of patterns of magnetism, the known cardholders offer no method of 'keeping' (in magnetism ter- minology) the magnetic patterns. The present invention is characterised by incorporating into the cardholders, keepers (1) in the form of sheets of magnetically soft ferromagnetic material with high resistance. The benefit of the invention is obtained when de- vices are placed with the reading surface of their magnetized stripes in close contact with the surface of the ferromagnetic materi- al which, making use of known properties of the material, then acts as keeper of the magnetic patterns.