A reading head is presented for use in a security system for reading an intermittent code pattern, when the code pattern is displaced in a reading direction with respect to the reading head. The code pattern is formed of a plurality of spaced-apart magnetic elements made. The reading head comprises a magnetic material producing a high-gradient static magnetic field, and a sensing element of a kind responsive to signals produced by the magnetic elements. The magnetic material is designed such that it defines an extended narrow region where the static magnetic field vector is substantially equal to zero. The sensing element is located substantially within the zero-field region, and is thereby responsive to signals generated by each of the magnetic elements, when the magnetic element is located in the zero-field region.