Safety Check isn’t a new feature for Facebook. In fact, Mark Zuckerberg introduced it to the social platform over a year ago. However, it wasn’t until the Paris attacks on Friday night that many started noticing an unfamiliar notification confirming the safety status of their friends located in the area: “[Friend’s Name] was marked safe during Paris Terror Attacks.”

The tool allows users to check in on friends during a disaster or crisis. Facebook describes it as “a simple and easy way to say you’re safe and check on others.” Which was a welcome relief for those with friends and loved ones in or around Paris during the tragic attacks that took at least 129 lives and left 352 injured. According to The Huffington Post, as of last night 4.1 million people had checked in as safe using the feature in the 24 hours since it launched.

Credit: Cosmopolitan