The National Rifle Association, in an article published on the blog of its political arm, wrote that “smart guns,” a term it mocks as a misnomer, have the potential “to mesh with the anti-gunner’s agenda, opening the door to a ban on all guns that do not possess the government-required technology.”

Mr. Keane said the industry did not oppose developing the technology. But, he added, “No. 1, the technology is not ready. No. 2, we believe the market ought to work.” Of the Armatix episode in California, he said, “They tried to put the product on the market, and the market reacted.”

Armatix said it had an agreement with the Oak Tree Gun Club, a large gun range and retailer about 20 minutes north of Los Angeles, to sell its iP1 pistol, which can be fired only after the owner enters a five-digit PIN into a watch that transmits a signal to the gun. The gun, which retails for about $1,800, disables itself if it is more than 10 inches from the watch.

But once Oak Tree’s owner, James Mitchell, went public in The Washington Post saying the iP1 “could revolutionize the gun industry,” Second Amendment activists went into overdrive, flooding social media with threats to boycott the club. They took to Calguns.net, a forum for gun owners, and called for vigilante-style investigations of Ms. Padilla and Armatix. They seized on her appearance before a United Nations panel to testify on gun safety and her purported association with a group once led by a protégé of George Soros.

“I have no qualms with the idea of personally and professionally leveling the life of someone who has attempted to profit from disarming me and my fellow Americans,” one commenter wrote.

Ms. Padilla found that any trace of her involvement with Oak Tree had vanished. Signs outside the club advertising Armatix had been taken down. Her branded merchandise — hooded sweatshirts, down jackets (camouflage for men, hot pink for women) — was gone. Her stall at the shooting range where she had shown prospective customers how the iP1 worked, once painted in her company’s signature blue, had a fresh coat of green paint over it. “Honestly, I was in disbelief,” she said. “It’s like I never existed.”

Mr. Mitchell disavowed his relationship with Armatix and denied ever selling the gun. Oak Tree officials did not respond to several requests seeking comment in person and by phone. When a reporter visited the club recently, an employee said, “I don’t know if we’re making any comments.”

Ms. Padilla and Armatix continue to look for stores to carry their pistols. She said she receives emails all the time from people asking her where they can buy one. But she cannot always be sure who might be a potential buyer and who might be just another person looking to harass her. “This is my mission in life,” she said, vowing to keep looking for customers. “If they really understood our technology, they wouldn’t be afraid of it at all.”