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MUSCATINE, Iowa – It’s the last thing a teacher wants to have to think about; what to do in case a shooter is in the school.

Mass shootings like the one at Sandy Hook Elementary and the most recent, a shooting at an Oregon high school Tuesday, inspired some Iowa middle school teachers to invent a device that just might save your child’s life.

The Sleeve” 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 Nitzel, 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,” Nitzel said.

“I can tell you in our training, all five rooms that the teachers were trained in; the doors were breached, the cords were ripped, and the officer who was portraying the active shooter came in and killed all of us,” Nitzel said.

That’s when Nitzel and his colleagues formed the company, Fighting Chance Solutions, and started designing blueprints.

“The Sleeve” is lightweight and compact so it can be quickly applied and removed from the door’s opening mechanism in case of an emergency.

It also allows the teachers to keep the door closed without having to go into the hallway to lock it from the outside, keeping them safe from harm, WQAD reported.

“I think it’s a great product. It’s going to buy kids and teachers time for shootings,” Muscatine Police Chief Brett Talkington told WQAD. “These shooters [are] going to be pulling on the door. If they can’t get in, they’re going to move on.”

MORE: Get more information on “The Sleeve” from WQAD