Cristy Thomas began to panic as she called 911 for the second time on a warm October day but couldn’t get through. She anxiously watched the plume of black smoke pouring over her rural community in central California get larger. Then she heard a familiar ping. Watch Duty, an app that alerts users of wildfire risk and provides critical information about blazes as they unfold, had already registered the fire. She relaxed. The cavalry was coming. “I can’t tell you the sigh of relief,” she said, recalling how soon after sirens blared through the neighborhood and helicopters thundered overhead. “We