Facebook and its never-ending list of features encouraging you to share even more about your life can be an easy target for critics. But when it gets it right — like giving you a place to check in on loved ones in a crisis zone — it really gets it right.

Facebook activated its Safety Check feature Friday afternoon just hours after numerous terror attacks in Paris left dozens dead and dozens more missing or held hostage. The feature rolled out a year ago, but many people are still discovering it for the first time. That’s a good thing, though, as the alert is only activated during events like natural disasters or attacks. Facebook uses geolocation information to identify people who live or are traveling in a disaster area, and then asks those people to check in on Facebook to alert friends and family that they are safe.

It’s a relatively simple but extraordinarily helpful way of using the social networking app we’ve all adopted. In this instance, you can check on your friends from Paris by clicking here.

Facebook has activated Safety Check five times in 2015, including after the Nepal earthquake back in April and the Chilean earthquake in September. When the feature launched, it was primarily presented as a tool for natural disasters, not those caused by human hate. But Safety Check is activated by Facebook, which means it can (and should) be used when needed. This is the first time it has been activated for anything other than a natural disaster.

It’s unclear how many people Facebook identified as being in the danger zone on Friday. We’ve reached out for comment and will update if we hear more information.

Update: A Facebook spokesperson responded with the following statement but did not share any details on how many people from the disaster zone were prompted to check in.

“We are shocked and saddened by the events unfolding in Paris. 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.”

Update: Facebook says that 4.1 million people in and around Paris marked themselves as “safe” within 24 hours of its activation. The company also claims that 360 million people were notified that friends had been marked safe.

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