A group of Silicon Valley technologists who were early employees at Facebook and Google, alarmed over the ill effects of social networks and smartphones, are banding together to challenge the companies they helped build. The cohort is creating a union of concerned experts called the Center for Humane Technology. Along with the nonprofit media watchdog group Common Sense Media, it also plans an anti-tech-addiction lobbying effort and an ad campaign at 55,000 public schools in the United States. The campaign, called the Truth About Tech, will be funded with $7 million from Common Sense and capital raised by the Center for Humane Technology.