Unstable rock slopes pose significant hazards, requiring reliable monitoring for effective mitigation. However, existing methods often struggle to capture the dynamic nature of these environments, highlighting the need for enhanced monitoring techniques. This study investigates the Brienz/Brinzauls landslide in Switzerland to deepen our understanding through passive seismic techniques. The objective is to gain insights into the evolving seismic response of active slopes before, during and after collapse events, thus, filling gaps in our understanding of the dynamics of the seismic response of landslides. We deployed automated tracking of seismic parameters spanning 5 years (2018–2023) and covering a partial collapse of the landslide, and tracked resonance frequencies, seismic amplitudes, wavefield polarization, and seismic event occurrences. In addition, we compared the seismic parameters with geodetic surface displacement rates. Over the 5 years, significant seismic parameter shifts were observed associated with increased rock fall events, resonance frequency reductions, and changes in wavefield polarization. Immediate seismic responses during and post-collapse in June 2023 gradually reverted to pre-event conditions within 2 weeks. This study provides new data-driven insights into unstable rock slope behavior, potentially contributing to the development of new ways of seismic early-warning systems. It emphasizes the necessity of ongoing and future monitoring efforts to accurately anticipate future landslide incidents, given the degree of uncertainties in the parameters monitored, for example, caused by transient seismic signals.