BEVERLY HILLS, Calif. — Belinda Padilla does not pick up unknown calls anymore, not since someone posted her cellphone number on an online forum for gun enthusiasts. A few fuming-mad voice mail messages and heavy breathers were all it took.

Then someone snapped pictures of the address where she has a P.O. box and put those online, too. In a crude, cartoonish scrawl, this person drew an arrow to the blurred image of a woman passing through the photo frame. “Belinda?” the person wrote. “Is that you?”

Her offense? Trying to market and sell a new .22-caliber handgun that uses a radio frequency-enabled stopwatch to identify the authorized user so no one else can fire it. Ms. Padilla and the manufacturer she works for, Armatix, intended to make the weapon the first “smart gun” for sale in the United States.

But shortly after Armatix went public with its plans to start selling in Southern California, Ms. Padilla, a fast-talking, hard-charging Beverly Hills businesswoman who leads the company’s fledgling American division, encountered the same uproar that has stopped gun control advocates, Congress, President Obama and lawmakers across the country as they seek to pass tougher laws and promote new technologies they contend will lead to fewer firearms deaths.