This book provides a comprehensive account of how mobile-smartphone systems are rapidly transforming public alert and warning in the United States. Recent events have vaulted mobile alert and warning technology to the forefront of public debates concerning the hazards of the digital age. False alarms of ballistic missile attacks on Hawaii and Japan, the non-use of mobile alerts during the Northern California wildfires, and the role of technology in supporting police manhunts and counterterrorism efforts have prompted reconsideration of how these systems are used. With interviews of officials, executives, experts, and citizens, the book provides an in-depth analysis of the events and contexts influencing the trajectory of mobile public alert and warning and charts a course for its improvement. Introduces the high stakes in transforming public alert and warning, and includes case studies that illustrate issues of risk, trust, and appropriateness in mobile public alert and warning.