Facebook launched a feature so that people in Paris can let their network know they are alive on Friday after at least 100 were feared killed following multiple terror attacks across the French capital and a hostage crisis at a rock concert in the Bataclan theater that prompted President François Hollande to shut down the country’s borders and declare a state of emergency. The social network’s “Safety Check” tool here asks users if they are in the affected area and enables them to “mark” themselves as “safe.” Then their Facebook friends will receive a notification.