DACULA, Ga. — The idea came to her in the vulnerable early morning hours, just after the horrific shooting at Sandy Hook Elementary in Newtown, Conn., nearly two years ago.

Celisa Edwards, a teacher, was shaken. What if a gunman burst into her school in this small town outside Atlanta? She could follow lockdown procedures. Turn off the lights. Lock the door. But that didn’t seem like enough to protect her seventh graders. Edwards had an idea. She hastily sketched it out and, a couple of hours later, woke up her husband. We need to make this, she told him.

The result was a simple metal wire with looped ends that could secure classroom doors from the inside. The Portable Affordable Lockdown System, patent pending, has been installed in one Georgia school. Edwards recently pitched it to another district.

Now, Edwards — whose only previous inventions involved devising lesson plans — was discussing her device with evangelical fervor during a free period late last week at Dacula Middle School. About the same time, hundreds of miles away in Maryville, Wash., a high school was going on lockdown after a student fatally shot two people and injured four others (one of whom later died). Almost immediately, the question, “What could’ve been done to prevent this?” was in the air.

“Our classrooms are not safe. There are people bent on doing wrong, doing evil,” Edwards says. “And we are deterring those perpetrators.”

A flood of school-safety inventions have hit the market in recent years, many of them created by novices stunned by what happened at Sandy Hook, where a gunman fatally shot 20 young students and six staff members in 2012. Since then, teachers and parents have come up with a range of door barricades, bulletproof backpacks, ballistic whiteboards and online apps to monitor for homicidal plots. These products join a school security market that is expected to reach $720 million this year, according to research firm IHS. And the dozens of school shootings that have occurred since Sandy Hook only ramp up the hunt for a solution.

Although they could be dismissed as profiting from tragedy, inventors such as Edwards say they are motivated by fear and a sense that policymakers have failed to safeguard students and teachers.

Kenneth Trump, a national school safety consultant, understands the attraction of the inventions. People felt helpless after Sandy Hook, he said. And there was a major push to “do something.” But the national debate over how to prevent school shootings soon stalled out, grounded mostly by ideological divisions over gun control. And into that gaping void went these inventions, many of them focused on hardening a school’s defenses. But Trump said he doubts that door locks and bulletproof materials would make a difference.

“What’s really being sold here is an emotional security blanket,” he said.

But that hasn’t slowed the sales of ballistic whiteboards, made by a company in Pocomoke City, Md., that crafts anti-IED armor for the U.S. military. The small, handheld whiteboards can act as defensive shields to fend off a gunman. George Tunis, chief executive of Hardwire, said the Sandy Hook shooting convinced him that his company had a role in protecting schools.

“That’s when it hit us, that these are fast events, and the armor needs to be in schools,” Tunis said.

Hardwire’s whiteboards, which sell for $399, are in nearly 1,000 schools in 50 states, he said. Later this week, the Colonial School District in New Castle, Del., will introduce its 121 whiteboards for use in classrooms.

In Jefferson Hills, Pa., a school maintenance man invented an emergency door lock after the Sandy Hook shooting. Students at Banneker High School in Washington, D.C., won a grant to develop a sleeve that jams a door’s hydraulic closer. A group of teachers in Muscatine, Iowa, formed Fighting Chance Solutions to sell something similar. A company in Burlington, Vt., released its Social Sentinel app to scour social media for signs of a school threat. And a father in Williamston, Mich., created The Boot, a steel bar that blockades a classroom door.

Robert Couturier had been kicking around that idea a few years before Sandy Hook happened. He started a company, which now has 14 full-time employees. Last week, he hired two more salesmen. He invented The Boot because he was tired of hearing about school shootings.

“I had to come up with a solution,” Couturier said.

Hardwire LLC, a Maryland company, sells a ballistic whiteboard made of military-grade anti-IED armor that can be used by teachers to shield themselves and their students from handgun and shotgun bullets and knife blades. (Hardwire LLC)

Since the Sandy Hook shooting, much of the discussion has been about whether to arm teachers. Many states introduced bills to allow guns in schools, but only a handful enacted laws specifically allowing firearms in public schools. One of them was Georgia, which earlier this year began allowing licensed gun owners to carry weapons inside bars, nightclubs and schools.

Trump, who has worked as a school safety consultant for three decades, noted how different the response was following the 1999 Columbine High School shooting in Colorado, where 12 students and one teacher were killed. Back then, the discussion focused on training school officials to spot warning signs and offering mental health support services. But these initiatives take longer to roll out and require sustained investment, he said. The emotional intensity of the Sandy Hook shooting seemed to demand a quicker fix.

“People are frustrated that there have been so many steps taken and they still have this happen,” Trump said.

Back at Dacula Middle School, Edwards was demonstrating her invention. Her seventh graders had just filed out of the room, walking past a ball python curled up in a glass enclosure by the door, after their discussion of the Theodore Taylor book “The Cay.” Edwards, 48, had energetically read aloud passages.

Now, she used that same intensity to show off her device. The wire rope was about two feet long and encased in plastic. Each end was looped, with a carabiner at one end. A metal eye hook had been drilled into a concrete-block wall, near a hand-crank pencil sharpener.

Edwards quickly hooked one end around the door handle and latched the other to the eye hook. The door was secure. No one was getting in or out. The door handle had a lock, but Edwards pointed out that administrators had keys that a gunman could take. Her simple invention had solved that problem.

“Teachers find solutions to problems. And my passion is for classroom safety,” she said. “That’s why I designed this.”

After her demonstration, Edwards slipped the device back into a small green bag and returned it to its familiar spot in her desk drawer, so she’d know exactly where it was, if she ever needed it.