Flash floods and landslides in Rwanda claimed 131 lives and cost €400 million in May 2023 alone. A lack of accurate rainfall data hampers the ability to issue timely warnings and prevent these increasingly frequent disasters. SENSOR² will establish a multi-stakeholder, multi-institutional partnership to introduce an innovative and cost-effective rainfall monitoring system using mobile phone network antennas. These unprecedented, nationwide rainfall data will be integrated in updated, accessible early warning systems and will be used to support research on nature-based prevention measures in the rapidly expanding city of Musanze. SENSOR² will bring together academia, government bodies and the private sector to design targeted solutions towards the most vulnerable communities in rural and urban Rwanda.