Magnetorheological composites made of iron micro-particles dispersed, near the percolation threshold in an elastomeric polymer, exhibit the concomitant effects of piezoresistivity and elastomagnetism, and their optimization can be obtained by a proper combination of the particle size, shape, volume fraction, magnetic permeability and electrical conductivity. In this material, the application of a magnetizing field produces a sample strain (elastomagnetism) and a consequent change in resistivity (piezoresistivity), namely the magneto-piezoresistive (MPR) effect. A magneto-piezoresistive ratio (resistance change/ magnetic field gradient) higher than 1000 Ωm/T has been demonstrated. The main objective of this paper is to determine the potentiality and limits of the MPR effect in detecting the change of magnetic polarization direction at magnetization intensity similar to those of a magnetic memory. Considering the possibility to miniaturize the MPR samples, this investigation constitute a basic step to open new perspectives in the field of magnetic read heads.