A modernized device intended for diagnosing the temperature dependent activity of cells is described. The activity of cells was determined by finding the correlation coefficient of optical signals in speckle patterns recorded at different moments of time. It is shown that, as the temperature increases from 26 to 36°C, variations in the optical paths in cells increase from 16 to 26 nm. This is probably associated with the physiological activity of cells-trapping of large molecules or their conglomerates. In contrast to the pre vious variant of the device design, instead of a lipid membrane, a cell monolayer was used, which was culti vated on a plane-parallel glass plate. In order to reduce variations in the optical path lengths in a nutrient solution, a 1.7 mm thick plane-parallel glass plate was additionally inserted into the cuvette. The modern ization of the device also includes heating of the cuvette with hot air flows.