The police and public prosecution may use methods to obtain information about the crime and the perpetrator during the investigation that significantly infringe on the rights of the accused or individuals associated with them. To legally secure these early interventions, their authorization is generally reserved for a judge. The empirical study, based on file analyses and interviews, examines how the legally mandated judicial reservation regarding telephone surveillance is implemented in practice. It finds that judges almost always approve surveillance requests and that the judicial reservation rarely relies on an independent decision by the judges, as required by the Constitutional Court.