PLOS Medicine April 12, 2016Surveillance is critical to manage preventative health services and control infectious diseases. Integrated surveillance involving public health, veterinary, and environmental sectors is urgently needed to effectively manage zoonoses and vector-borne diseases. However, most surveillance in low-income countries is paper-based, provides negligible timely feedback, is poorly incentivised, and results in delays, limited reporting, inaccurate data, and costly processing. • The potential of mobile technologies for improving health system surveillance has been demonstrated through small-scale pilots, but large-scale evaluations under programmatic implementation remain rare. • An intersectoral mobile-phone–based system was developed and implemented for rabies surveillance across southern Tanzania. Since 2011, the system has facilitated near realtime reporting of animal bites and human and animal vaccine use (almost 30,000 reports) by over 300 frontline health and veterinary workers across a catchment area of 150,000 km2 with >10 million inhabitants, improving data quality, timeliness, and completeness while reducing costs. • The surveillance system infrastructure is a platform that can be further developed to improve services and deliver health interventions; for example, generating automated personalized text messages (SMS) to alert patients to their vaccination schedules improved their compliance with regimens. Other interventions targeting patients and health workers can now be implemented easily. • The system has become an integrated, popular, and valuable tool across sectors, used routinely throughout southern Tanzania to evaluate the impacts of rabies control and prevention activities and to improve their management, directly informed by the experiences of frontline users. • We discuss challenges encountered during development and deployment, how we overcame these, and our recommendations for scaling up mobile-phone–based health (mHealth) interventions in low-income countries.