In the technical field of known cardholders for devices such as cards with magnetic stripes on which is encoded information and/or data in the form of patterns of magnetism, the known cardholders offer no method of 'keeping' (in magnetism terminology) 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 devices are placed with the reading surface of their magnetized stripes in close contact with the surface of the ferromagnetic material which, making use of known properties of the material, then acts as keeper of the magnetic patterns.