One high schooler has come up with a device to prevent active shooters from getting inside classrooms – and to keep students safe.

He calls it the "JustinKase." It's a product made of steel that latches to a door frame to bar entry.

“Unlike other products, JustinKase does not allow a door to open even a crack which means students & staff can remain safe while emergency personnel race to the scene,” creator Justin Rivard, a student at Somerset High School in Wisconsin, explains on his website.

Rivard came up with the idea for the safety product, which he sells online for $95, two years ago – when he was just 15. He spent months refining it.

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“You can lock a door with a lock, it can get shot out,” Rivard told KARE. “You can lock a door with this, it can’t get shot out. You can’t get around it.”

The 17-year-old is now reaching out to schools to spread the word about his product.

His own school already ordered 50 of them, one for each room in the building, according to KARE.

“We immediately, within a week of having these, went through an entire drill, all throughout the building, really walking through students and staff,” Somerset's principal, Shannon Donnelly, told KARE.

Wisconsin's Grantsburg School District also ordered more than 50 devices.

Rivard has yet to discover anyone able to open a classroom door when JustinKase is set up.

“He truly believes that this device is going to save lives,” Donnelly said.

Rivard said he hopes no school will actually have to use it, but "just in case you need it, it’ll be there," he told KARE.