Fighting Chance Solutions (FCS), the company Nietzel founded with his six colleagues, launched the product with a small press conference in Muscatine, Iowa, on June 10. That same day, in an unfortunate coincidence, a teenager opened fire in a school in Oregon, killing another student and then himself. The tragedy propelled the story of the Sleeve into the national media.

The first Sleeves were bought by the local community college, and since then, the company has been contacted by other colleges, military institutions, and schools around the country and abroad. As well as addressing teachers’ fear, the invention offers a solution to a problem all these institutions are facing: how to make doors lockable from inside without replacing them. The company is now fielding orders ranging from single units (purchased directly by teachers) to tens of thousands (several school districts have expressed interest).

Nietzel and his colleagues came up with the idea for the Sleeve after a teacher-training last fall, where they were advised to try and keep the door closed by tying a computer cord or a belt around the door closer arm on top of the door—an infuriatingly ineffective method, he said.

Indeed, during the demonstration, teachers tried this approach in five classrooms, but a man simulating a shooter was able to enter the room each time. “I kept thinking…in this day and age, in the 21st century, what you want us to do is tie a knot around the door closers? And essentially you tell us ‘If it doesn’t work, good luck’?'” he said.

It took about 10 months for FCS’s team, with the help of architect and engineer friends, to go from the first prototype of the Sleeve (made out of a rubber container) to the fourteenth, and final, model.

A single-purpose tool, the sleeve sells for $65—more palatable than the estimated $300 to $600 that FCS estimates would be needed to replace a door with one that it could be locked from the inside. The company is marketing it directly to teachers, so that they don’t have to wait for the district or school to purchase the device, says Nietzel. The company is also offering bulk ordering, but he said school districts can be slow to react.

Nietzel says he envisions teachers carrying the sleeve in a purse, or having it in their drawer, rather than keeping it on display. After the door is secured, the teacher can try to calm down the kids in the classroom, he said, and help them to safety, whether that means “evacuating out the window, or staying on the floor where they can’t get shot.”

The Oregon shooting increased the attention to the product as it was launched, he said: “The reporters were all still there and they were holding the product in their hands, and they were watching the school shooting unfold, and you could see that it really had a profound effect on them.”

The FCS members, who didn’t expect the product to be this successful, are taking advantage of their summer break to work on their venture full-time, which is also bringing business to the community: The manufacturer, Fabricators Plus, employs 125 people. “We are 100% based out of Musketeen Iowa—from the people who make our product to the people who make our polo shirts when we go out and talk to people,” Nietzel said.

Nietzel does not plan to turn into a full-time entrepreneur just yet, but he doesn’t rule it out. “I never want to leave education, but I also understand that there might be a time where I need to dedicate a little more time to this and to student safety.”

📬 Sign up for the Daily Brief

Our free, fast, and fun briefing on the global economy, delivered every weekday morning.