20,000 volunteers across the U.S. measure precipitation: when extreme weather hits, emergency managers turn their data into life-saving alerts. Armchair mappers worldwide update information used by first responders after the Nepal earthquake. A new project, EyesOnALZ, enlists the crowd to speed up research on Alzheimer's disease. DIY enthusiasts from Public Lab map the BP oil spill with kites, balloons and cameras and continue to watchdog pollution. The crowd, using mobile tech and the cloud contribute to science that saves lives.