After what's now being called the worst mass shooting in U.S. history, people are scrambling to see if their loved ones are safe in Las Vegas. Facebook is one resource that can quickly do that for you from your phone.

Facebook's Safety Check is a feature that is automatically activated in your area if enough people are posting about an emergency. You'll get an automatic notification on your Facebook app to "Let Friends Know You're Safe" which will then say you are "Marked Safe" at said emergency.

If you have a friend or loved one in Las Vegas currently and are wondering about their whereabouts, this page popped up for a friend of mine who resides there this morning. Luckily, he's fine. Had the notification not popped up on my Facebook, I wouldn't have known his status.

Obviously, in the event of an emergency, the last thing you should be thinking about is your Facebook. However, it can be a vital resource for both those near an emergency and those wondering about them.