This paper delves into the dynamics of popular revolt in early modern Castile, taking as a viewpoint a revealing feature of these disturbances, the bell-ringing widely known as rebato, an equivalent to the French tocsin. While alarm bells have long been recognised as a prevalent element of popular revolt in Europe from medieval times, they have received limited specific scholarly attention. This study provides an overview of the historical significance of this distinctive sound and examines its material aspects. Subsequently, the paper investigates several instances of bell-ringing during Castilian riots, as reflected in archival sources, and analyses its meaning both for townspeople and the authorities. In attempting to elucidate the reasons behind the aversion this sound provoked among the privileged classes and the authorities, the study explores the political, ritual, and sonic dimensions of the rebato.