Here we report on the magneto-optical Kerr effect employing a nematic liquid crystal (LC) device as an optical modulator. This device allows performing intensity, phase, and polarization modulated measurements with a huge signal-to-noise ratio when compared to those obtained by means of an opto-mechanical chopper and a photo-elastic modulator. The results demonstrate that the optimal performance is achieved modulating the polarization state of the incident light by means of the LCs.