But Mr. Sheikh acknowledged that the backpacks were less effective at blocking gunfire from powerful semiautomatic weapons, like the ones used at Sandy Hook. And gun-control advocates say there is no evidence that armored backpacks, however carefully tested, would keep children safe during a shooting.
“We’re asking children to stand up to gunmen because lawmakers are too afraid to stand up to the gun lobby,” said Shannon Watts, the founder of Moms Demand Action for Gun Sense in America, a grass-roots gun-control organization. “There isn’t a parent in this country that isn’t terrified. These companies are capitalizing on that.”
Mr. Siboni, who runs ArmorMe, said it was unfair to accuse his company of exploiting national fears about gun violence to turn a profit.
“Whatever you do, you’re capitalizing on something,” he said. “We are just responding to a need.”
In several recent Twitter posts, Senator Kamala Harris of California, a Democratic presidential candidate, has held up bulletproof backpacks as a symbol of the broader problem of gun violence in the United States.
“Parents shouldn’t have to buy a bulletproof backpack for their child just to keep them safe in school,” she tweeted in July. “This shouldn’t be normal.”
But for Celeste Green, a senior at the College of Charleston in South Carolina, the backpacks seem like a necessary precaution.
The day before the shooting in El Paso, Ms. Green, 22, learned that a teenager in her hometown, Columbia, S.C., had threatened to “shoot up” a local school. When she saw the news, she thought of her younger sister, who is starting high school in the fall. Ms. Green sent her mother a few videos and hyperlinks with information about bulletproof backpacks.
“Immediately, she was like: ‘Where should I start? Where should I look?’” Ms. Green said. “There was no question.”