There is provided a reader for reading information magnetically coded on a carrier. The reader includes a magnetizing device for magnetizing the information precoded on the carrier and a transducer for detecting the magnetized information as the carrier is translated successively past the magnetizer and transducer. The magnetizer includes at least one magnetic layer having a succession of adjoining zones, the length of alternate zones being much greater than the length of the other zones and the magnetic induction in the zones being of opposite sense. The transducer includes at least one magneto-resistive detecting member and a magneto-resistive compensating member which are of anisotropic magnetic material. The members are disposed to develop across the compensating member a voltage in response to the interference magnetic field which is equal to that developed across the detecting member due to that field. However, the compensating element is positioned so as to be outside of the magnetic leakage field of the coded information. The leakage field of the magnetizing device is utilized to polarize the magnetic-resistive members by causing their axes of easy magnetization to rotate through an angle .theta. between 0.degree. and 90.degree. and preferably 45.degree..