Our culture contributor Britt Julious was waiting to enter a rain-delayed Lollapalooza in Grant Park today when she received a curious alert on her Facebook app—her cousin had just marked herself "safe" during what Facebook labeled "violent crime in Chicago, Illinois."

Facebook said the event happened around 1 a.m., indicated an area that was miles away from her current location, and asked if she wanted to mark herself safe as well.

Minutes later, the option to check in disappeared and Facebook said the safety check had been turned off.

Social media posts around the city show some people confused about the reason for the alert or reacting to generic nature of the message.

A Facebook spokeswoman said the alert was community-generated, meaning that an algorithm had detected multiple Facebook statuses posted in a small geographic area about the same event. The algorithm's findings are checked against a third-party security company that provides data on major incidents throughout the country, including shootings and airport closings. In this case, the violent crime was a shooting in the Back of the Yards neighborhood, which left two people dead from gunshot wounds. A 16-year-old girl later died due to an asthma attack after witnessing the shooting.

Once the algorithm notices an event, it prompts people who posted related statuses to mark themselves as safe, and allows them to ask friends to check in as well. (Julious says her cousin, who was miles away from Back of the Yards at the time, received the notification from a niece.)

That's how someone in Grant Park this afternoon received a notice about a crime that happened hours ago near 51st and Halsted.

The Facebook spokeswoman says that more generic language like "violent crime" is used when an incident is not yet verified and specific language might cause panic. She says "violent crime" community-generated checks have been activated three times in the past two weeks—in Alberta, Canada; Bastrop, Texas; and during the shootings of police officers in Dallas.

Once more information is confirmed, Facebook may choose to activate a more formal safety check where everyone in a certain geographic location will get a push notification to check in—something that didn't happen in this case, but did, for instance, in Orlando during the mass shooting at a nightclub that left 49 people dead.

Facebook emphasizes that the community-generated alert is an automatic feature that doesn't imply any sort of judgment on the event, but rather relies on the reporting of Facebook users themselves and their friend networks.

Dorothy Wright, Julious's cousin who checked in, says she got the notification this morning after she arrived at work downtown. The 54-year-old says it was the first time she had seen something like that. (Facebook is checking to see if it's Chicago first safety check; the community-generated feature just became available two months ago.)

Wright says she assumed the "violent crime" was a robbery or a shooting, though the message did not alarm her. She says she heard about the Back of the Yards shooting on the news this morning but did not connect the two.

It's possible this particular shooting stood out because of news that a teenage girl died from an asthma attack after witnessing it. Though double homicides are not uncommon in Chicago, the added impact of a witness dying may have caused more people to post about it on Facebook.

Corey Hardiman, 25, says he received a notification after arriving at work at Paul Robeson High School in Englewood this morning. The CPS educator felt at first that Facebook was making a kind of statement, "like gun violence is so out of control that it's being considered a natural disaster," he says.

"At first it kind of catches you off your guard, because you think, why are you checking in?" he says, adding that neighborhoods that are plagued with gun violence deserve more attention at a national level. "But then some people thought it was like another add-on to Facebook, not a warning to others."

Facebook says that since the feature is relatively new, users are still getting used to seeing it and understanding what it means: "We are continually working to find the best way for Safety Check to be helpful to the most people. We'll continue to test and improve the ability for people within the community to activate Safety Check."

It's not the first time Chicagoans have received safety check notifications or talked about needing them. A glitch earlier this year led some Chicagoans to check in during an explosion in Pakistan.

Facebook previously only used the safety check feature for natural disasters, but began expanding the usage during the Paris terrorist attacks last November. Since then it's been a sensitive topic, with critics wondering why certain disasters prompted the larger geographic-based safety check while others did not.