In Paris, at least 129 people are reported dead in coordinated attacks at six locations. If, like me, you live in the U.S. and have friends and family abroad, your first thought is likely whether or not they're safe, where they are and who they're with.
Facebook has responded quickly to the Paris attacks. A feature called Facebook Safety Check, first released in October 2014, started to pop up almost immediately after Friday's news broke. It allows you to notify friends with your safety status, view which of your friends are in the affected area and even mark others as safe.
It's easy to use. Tap this link. Facebook will ask you, "Are you in the affected area? Let your friends know you're safe." Tap the button below that: "Yes, let my friends know."
Here's what it looks like on desktop and mobile. You can opt to see only friends marked safe, friends who haven't checked in or all friends in the area.
To figure out where you are, Facebook uses the city you've listed in your profile and your last recorded location, if you allow Facebook's Nearby Friends feature to use GPS data to track where you are.
The backstory: "In times of disaster or crisis, people turn to Facebook to check on loved ones and get updates," Facebook wrote in a blog post in October 2014. "It is in these moments that communication is most critical both for people in the affected areas and for their friends and families anxious for news."
Facebook said it was inspired by how users turned to social media after Japan's 2011 earthquake and tsunami.
Our engineers in Japan took the first step toward creating a product to improve the experience of reconnecting after a disaster. They built the Disaster Message Board to make it easier to communicate with others. They launched a test of the tool a year later and the response was overwhelming.
In the aftermath of Superstorm Sandy in 2012, many users created Facebook pages to send updates and locate missing belongings.
On Friday, the year-old tool proved to be a popular, inestimably helpful feature and an unexpected blessing for many American users. Several people I spoke with hadn't heard of or seen the feature before the Paris attacks. But the relief was palpable for anyone who opened Facebook and saw immediately that their friends were safe.
A Facebook spokesperson told Mic that this is the first time Safety Check has been used for a shooting; the previous five instances were for natural disasters. "We hope we never have to do this again," she wrote.
Nov. 14, 2015. 1:58 p.m. Eastern: This story has been updated.