News is still developing around a series of explosions in Brussels airport and subway, with at least 34 reported deaths and 230 injured so far. But if you might have friends or loved ones in the area, you don't have to sit back and idly wait for word.
After the phone networks buckled under the weight of communications in Belgium, people cried out for Facebook to turn on Safety Check, a feature that lets you mark yourself safe and notify your friends that you're ok in the wake of a disaster.
Facebook answered the call and activated its emergency service. Immediately, the notifications spilled in.
Safety check was originally designed to help people notify each other that they were safe and accounted for during natural disasters. The feature was turned on for the first time after the Paris attacks, and was used by 4 million people. Some wondered in the aftermath why it hadn't been turned on before for tragedies in non-Western countries like Turkey and Kenya.
How to use it: Safety check automatically looks to see if you or your friends are within the affected area — Brussels, in this case — and send you a push notification to log in and mark yourself safe:
Then, notifications will be sent out to all of your Facebook friends that you've marked yourself as safe. But even if you haven't received any notifications yet, there's a section of Facebook where you can see all of your friends who are in the area and manually mark yourself safe if you need.
Click here to get to that hub and see if you need to check in, check on friends in the area, or to tell someone you're safe.
March 23, 2016, 10:56 a.m.: This story has been updated.