It's horrible to think about, but if a gunman or other intruder is attempting to gain access to a classroom, the safest thing is to find a way to keep the person locked out.

A group of Iowa middle school teachers tackled that problem and invented a device that could save kids' lives, should the unthinkable happen.

Called “The Sleeve,” the device is a 12-gauge carbon steel case that fits around the door’s closer arm, securing the door from the inside. According to WQAD, “The Sleeve” can withstand more than 550 foot-pounds of force, making it nearly impossible to open from the outside.

WQAD reported Daniel Nietzel, a teacher at West Middle School in Muscatine, Iowa, got the idea from the school’s active shooter training.

“We were instructed to tie a belt or a cord around the closer arm. It seemed like a logical way to secure a door without having to go into the hallway, [but] it took us a long time to get a cord, stand on a chair, and tie a knot, which could potentially be the most important tie of your life,” Nietzel said.

Nietzel named his company “Fighting Chance Solutions.”

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