In observations close to the edge of the solar disk, the Ca II infrared triplet has a scattering polarization pattern at the level of 10-3 in its two strongest lines and at the 10-4 level in the weakest. This polarimetric sensitivity is now accessible with modern spectropolarimeters and scattering polarization has been observed by several authors in the Ca II infrared triplet. We discuss here the interest of observing these lines for the detection and mapping of magnetic fields in the quiet solar chromosphere. To this end, we investigate theoretically the sensitivity of the polarization pattern to the presence of magnetic fields through the Hanle effect. We find that the Ca II 8542 Å and 8662 Å lines are mostly sensitive to fields between 0.001 and 0.1 G, the former is also weakly sensitive to fields between 1 and 10 G. Otherwise the polarization signals are dependent only on the magnetic field geometry, but not on its intensity. The 8498 Å line is highly sensitive in the whole regime 0.001-10 G, but its polarization signal is much lower. Diagnostic diagrams giving the Q/I vs. U/I values at the line core for several magnetic field configurations and intensities are presented. We also discuss the sensitivity of the scattering polarization signals to the temperature gradient of the atmospheric model.