  We designed, constructed and have been operating a system based on
single-crystal synthetic diamond sensors, to monitor the beam losses at the
interaction region of the SuperKEKB asymmetric-energy electron-positron
collider. The system records the radiation dose-rates in positions close to the
inner detectors of the Belle II experiment, and protects both the detector and
accelerator components against destructive beam losses, by participating in the
beam-abort system. It also provides complementary information for the dedicated
studies of beam-related backgrounds. We describe the performance of the system
during the commissioning of the accelerator and during the first physics data
taking.
