Severe instability processes have affected the Rotolon catchment (Eastern Italian Alps) for long time. The first written proof of a landslide occurrence dates back to 1798. The last re-activation occurred in November 2010 when, after a cumulative rainfall of 637 mm in 12 days, a mass of approximately 320,000 m3 detached from the unstable slope and evolved into a debris flow that ran for about 4 km along the channel, threatening the villages along the stream. Since then, the design and the implementation of an early-warning system was considered of primary importance, in order to mitigate the risk for the valley inhabitants. A monitoring network consisting of 42 topographic benchmarks and 6 wire extensometers was installed and a warning system was deployed along four sections of the channel. The latter consists of 3 pendulum sections and a trip-wire section. Alarm sirens installed near the settlements are activated when the warning system is triggered by a debris-flow event, guaranteeing some minutes lead time to the local population. In this way the inhabitants could evacuate in time and reach safe areas thus reducing the risk. A Decision Support System (DSS) is also integrated with the deployed sensors, therefore technicians may support crisis response with a user-friendly instrument.