This Facebook Feature Kept People Connected During the Paris Attacks

After Friday night’s terrorist attacks in Paris, you may have noticed an unusual notification appear on Facebook for the first time: “[Friend’s Name] was marked safe during Paris Terror Attacks.”

The notifications came from a Facebook feature called Safety Check. If you’re in an area struck by some kind of life-threatening situation, Safety Check will prompt you to tell your Facebook friends you’re safe. To figure out your location, the feature looks at several data points, including your profile data, your last location (if you let Facebook see that information) and the city from where you’re connected to the Internet.

TIME’s Naina Bajekal reports from Paris the company sent her a text message asking to confirm her status during Friday’s attacks — text messages will often work even when full Internet access isn’t available.

Unlike a normal Facebook update, using Safety Check will instantly blast your status to your friends in the form of a notification. That’s a smart touch — this reporter received at least one such notification Friday from a friend he didn’t even know was in the area.

If you’re with other people, you can also mark them as safe. That’s handy if they don’t have the means to access their Facebook account in the midst of a chaotic or dangerous situation.

Facebook introduced Safety Check last year, inspired by an employee project built in the wake of the devastating tsunami that struck Japan in 2011. It was initially envisioned as a tool to use during natural disasters, like earthquakes or hurricanes. It’s been activated several times already for those incidents: I was notified of a friend’s safety following an earthquake in Afghanistan; the feature was also activated in April after a similar disaster in Nepal.

But Paris is the first time Safety Check was deployed during a terrorist attack.

“We are shocked and saddened by the events unfolding in Paris,” a Facebook spokesperson says. “Communication is critical in these moments both for people there and for their friends and families anxious for news. People turn to Facebook to check on loved ones and get updates which is why we created Safety Check and why we have activated it today for people in Paris.”

Contact us at letters@time.com.