In areas located near large rock cliffs, risk reduction by early warning monitoring systems highligts potentiality but also critical issues and limits. The paper examines two rock slope failures that occurred in a short time from each other near inhabited areas in the Italian Alps. The viscous behavior of the rock mass was reconstructed through data processing from ground-based Synthetic Aperture Radar Interferometry (InSAR), and elaboration of acceleration and speed curves. Landslides types and underlying complexity associated with rock detachment mechanisms suggest the identification of precautionary alarm thresholds for collapse forecasting. The analysis of financial outlay, both for mitigation works and for monitoring activities, highlight the adequacy and the opportunity to combine passive systems, like embankments or rockfall drapery meshes, with a reliable monitoring network for early warning.