In this paper, a new type of sensor for in-line measurements of antifreeze mass fraction in aqueous solutions is described. Its principles of operation are based on the exploitation of the temperature rise that accompanies the freezing of an undercooled solution. Measurements are performed on small volume samples, taken from a distribution loop. The device operates in batch and is reliable, compact and robust. Tests carried out with carefully calibrated water–antifreeze mixtures shows that its application fields are fully compatible with the antifreeze concentrations usually encountered in cold distribution circuits. This sensor can also be used for the experimental determination of the freezing point of various water–antifreeze mixtures, its accuracy being confirmed, with mono propylene glycol and mono ethylene glycol, by comparison of our results to those of the literature. However, tests carried out with ethanol showed that its performances are still to be improved with this antifreeze.