Since the late 1970s, the BirdLife Partnership has been working collectively to identify, document and protect places on the Earth with the greatest significance for the conservation of the world’s birds. As a result, over 13,000 Important Bird and Biodiversity Areas (IBAs) have been identified. However, we lack comprehensive monitoring of the condition of these sites, with an increasing number of IBAs under threat from damaging development – the majority of which appears to be poorly planned and does not take environmental values into account. Sites face a wide range of problems, which require an equally wide range of solutions. To address this problem, Natura Alert has been developed within the Horizon 2020-funded LandSense Citizen Observatory project. Natura Alert is a mobile app and web portal that allows users to pinpoint the location of threats to biodiversity and habitat changes, to prevent the further damage or loss to our biodiversity. We are particularly interested in threats that are occurring inside IBAs, Key Biodiversity Areas (KBAs) and Natura 2000 sites in the European Union, although submitting records in other areas is also possible. Information on the condition of these sites, the threats to them, the conservation measures in place and the changes in these aspects over time are essential to set priorities, hold governments to account and inform policies and decision-makers. Volunteers can share their observations with the wider community and help to map the state of our most valuable sites around the world. They can download our mobile app to quickly record their observations in the field or use the web app to discover more functionalities, such as visualizing reports from other users, creating dashboards per country and downloading their own reports. Natura Alert is being tested in Spain and Indonesia, thanks to the volunteer network of two BirdLife partners: SEO/BirdLife and Burung. While the Spanish volunteers are focusing on threats to birds and habitats within IBAs and Natura 2000 sites, the Indonesian communities are validating alerts from satellite-image analysis for forest change on Flores island. Citizen observations trigger real-time alerts to national and regional IBA/KBA coordinators at BirdLife International, who will ensure that the data are of high quality and produce regional and global monitoring assessments that could help monitor the indicators of the Sustainable Development Goals (SDGs) and the Convention on Biological Diversity (CBD). Also, researchers and practitioners around the globe can benefit from this type of data, as well as institutions and stakeholders from the private sector willing to make better decisions based on high quality data via the Integrated Biodiversity Assessment Tool (IBAT).