The inclusion of the biometric data, among them those of the digital impression, among the special categories of data foreseen by the RGPD it does not allow to go in an automatic way that the implantation of a system of hourly control based on the collection of this type of data can consider itself proportionate and, therefore, in agreement with the principle of minimization. It is necessary to make an evaluation of the impact about the data protection in view of the circumstances concrete in what the treatment is carried out to determine the legitimacy and the proportionality, included the analysis of the existence of alternatives less intrusives, and to establish the suitable guarantees.