Nature Cell Biology, Published online: 21 August 2026; doi:10.1038/s41556-026-02037-0 Lebrec et al. present a FRET-based cGAS reporter and show that cGAS activation by genotoxic stress is rare and uncoupled from micronuclei. The study implicates R-loop structures and subtypes of chromatin bridges as potential cGAS activators.