Facebook users in Orlando are being prompted to check in and let their friends know that they are safe, after 50 people were killed and another 53 were injured overnight at a popular gay nightclub in the Florida city.

Facebook’s “Safety Check” feature activates during major disasters and, increasingly, during terrorist attacks and conflict situations around the world.

In addition to allowing users to let all of their friends easily know that they are safe, it also provides people with a list of their friends whom Facebook thinks may be near the affected area. For Orlando, that list is available here.

Safety Check, launched in late 2014, was developed after the 2011 earthquake and tsunami in Japan as a quick way for people in the immediate area of a major natural disaster to let others know they are safe.

It was first used for a conflict situation last November, after the deadly terrorist attacks in Paris — prompting some controversy about why Facebook opted not to use the tool for other then-recent attacks in Beirut, Garissa, Kenya, or Ankara, Turkey.

According to Facebook, Safety Check was first activated this morning in Orlando by a “community-generated” effort, a feature the site said it began testing over the past month to “make it easier for our team to activate more frequently and faster, while testing ways to empower people to identify and elevate local crises as well.”

In addition to the Orlando shootings, Safety Check has been activated more than a dozen times since the start of 2016.