Facebook on Sunday activated its Safety Check feature for the first time in the US, after a gunman killed 50 people in an Orlando nightclub.

Safety Check lets users share their status and check on others during an emergency. Folks with online friends in the Orlando area may have received mobile or Web notifications over the weekend as people marked themselves safe in the wake of what is being called the worst mass shooting in US history.

"Waking up this morning, I was deeply saddened to hear about the shooting in Orlando," Facebook chief Mark Zuckerberg wrote in a post. "My thoughts and prayers are with the victims, their families and the LGBT community."

Safety Check emerged in the wake of the Japan earthquake and tsunami in 2011, but formally launched in 2014 for use during natural disasters—emergencies like hurricanes and tornados.

The social network was criticized after it activated the feature for the November terrorist attacks in Paris, but not for similar bombings in the Middle East. In response, Zuckerberg announced the function would be rolled out for all major disasters. In 2016, Safety Check has been turned on 17 times, compared with 11 times in 2014 and 2015 combined.

The weekend's shooting, however, marked the first US-based Safety Check—the first legitimate one, at least. In March, Facebook accidentally triggered the tool for United States-based users in response to a suicide bombing in Lahore, Pakistan.

"Earlier this month, we began testing features that allow people to both initiate and share Safety Check on Facebook," a company spokeswoman told PCMag in an email.

Related Facebook Alters Safety Check to Improve Accuracy

"Over the last few months, we have improved the launch process 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," the statement said.

Facebook has made its share of mistakes, including a Sunday gaffe that unintentionally declared the Philippines at war. In honor of Philippine Independence Day, Facebook's homepage greeted local netizens with a cartoon rendering of the country's flag. Except, the excited characters celebrating the holiday carried the flag upside down—the red stripe at the top, and the blue strip at the bottom: a sign that the nation is in battle.

"This was unintentional, and we're sorry," the tech titan told The Philippine Star. "We care deeply about the community in the Philippines and, in an attempt to connect people on Independence Day, we made a mistake."

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