The city installed more than 21,000 door alarms in public schools this past fall to protect young students from wandering out, but NY1 has learned three kindergartners walked out of their school last week, and it seems nobody noticed they were missing. NY1's Lindsey Christ filed the following report.

A demonstration of what's supposed to happen when an unguarded door opens in a city public school includes an alarm triggering a coordinated response by teachers, administrators and security guards, who quickly check the outside area for young children or students with special needs who might have walked out and could be in danger.

But this new procedure, with its multimillion-dollar alarm system, didn't work at PS 149 in Queens last week. Three kindergartners wandered outside Wednesday, and when they couldn't get back in, they walked to a nearby park. A passerby found them and returned them to the school. Police say they were never notified.

"They should have more attention, have more helpers around school, you know, especially for those kids, you know," said Eli Casiano, a parent of a student at PS 149. "Imagine if something wrong happened."

This is exactly what's not supposed to happen under Avonte's Law, passed in 2014 and named after Avonte Oquendo, the 14-year-old with autism who ran out of school in 2013 and whose remains later were found in the East River. Almost all of the city's 1,800 schools got door alarms to prevent other children from going missing. Ironically, PS 149 is in the same district as the school Avonte attended.

Parents say they're upset the school still hasn't told them about the new incident.

"It's a big deal. It's a big deal for me," said one parent. "I've got two kids in there."

The Department of Education said the three wandering students are now safe, and the city's special schools investigator says its opened an investigation into what went wrong.

Last spring, city investigators said complaints of children leaving schools or being left unsupervised had soared 75 percent in one year, with at least 160 cases of students simply walking out of school in 2014. The city said then that the new alarms would be a solution.

Editor’s note: An earlier version of this story indicated that the students who exited the school were second graders. NY1 has since learned that the students who exited the school were actually in kindergarten. The story has been updated to reflect this change.