Say you keep a firearm for home defense. Picture your small daughter finding your gun. If it's loaded, that could be the last thing she ever does.

It's not exactly a rare scenario. Firearm injuries were the second-leading cause of death among children in 2016, according to a study published in the New England Journal of Medicine.

Safety technology could make accidental firing impossible, at least that's what developers hope.

The technology exists. But after years of boycotts, political infighting and technological hurdles, it has yet to fully catch on. Now, developers are trying a new tactic to build a market: selling their products to police.

Unlocking your gun like you unlock your smartphone

Kai Kloepfer is the inventor of a fingerprint-activated 9 mm handgun called Biofire. Firearms like this are known as smart guns: They allow only someone they recognize to fire, without a trigger lock or attachment. The fingerprint technology is built into the gun.

At the Gun Safety Technology Expo in Milwaukee, Wisconsin, Kloepfer demonstrates how the technology works. There's a small light at the bottom of the pistol grip. When an unauthorized user tries to fire, it flashes yellow.

"If I try to pull this trigger, nothing is going to happen," Kloepfer says.

When he shifts his grip to hold the gun as if he were shooting it, lining his grip up with the fingerprint reader, the light in the base of the grip flashes green.

"That means it recognizes my fingerprint," Kloepfer says, "so if I try to pull the trigger, it'll fire."

But what if, when you really need to use your gun, the fingerprint reader doesn't accept your fingerprint?

Kloepfer acknowledges that skepticism about the technology is a daunting hurdle.

"One of the key things that we are going to prove with our product is reliability," said Kloepfer, after the expo. "Can you make an electrical system integrated into a mechanical firearm as reliable as that mechanical firearm just by itself? That's a major question."

So Kloepfer is waiting to go to market, taking years working out all the kinks and waiting until the time is right.

Smart guns like Kloepfer's do exist. Perhaps the most famous smart gun to recently make it to market, the Armatix iP1, was released in 2014. It included radio-frequency identification, or RFID, technology built into a .22-caliber, futuristic-looking pistol. Users were prevented from firing the gun unless they wore a custom-made watch with RFID.

Harsh reviews from the NRA about its small caliber and the technology, along with backlash from gun owners towards anyone who tried to sell it, prevented it from ever gaining traction.

Avoiding the mistakes of the past

The idea behind the gun safety expo was to connect a new round of inventors with police departments. Police departments buy lots of guns. And their opinions on firearms are well-regarded.

Erin Stilp, one of the organizers, started the expo by addressing a mistake of past attempts to get smart guns off the ground.

"It just has to do with making a safer gun that's not going to get a kid shot or a suicidal teen at the wrong time or a thief who's going to shoot a police officer," said Stilp, to a crowd of 150 or so police officers, inventors, investors and the media. "That's what this is about. This is not about the mandate."

The mandate she's referring to is a 2002 New Jersey law that requires gun shops to switch to selling only smart guns once a smart gun made it to market anywhere in the country.

After the law was passed, gun rights supporters worried about a wave of similar laws. And they boycotted gun sellers considering selling a smart gun. That put a quick stop to all kinds of technology meant to make guns safer.

"Yeah, I've lost people who would otherwise invest," said Ehren Achee, an engineer pitching an idea for a smart gun.

Instead of a fingerprint scanner, Achee's gun would use RFID technology, like the Armatix iP1. If your employee badge opens the door at your office, it uses RFID. An authorized user would wear a ring or a watch to unlock the gun and it would have to be close to a chip in the gun for the firearm to work.

Achee's looking for investors so he can make a prototype.

"The New Jersey law wasn't intended to kill this. It was intended to encourage it," said Achee. "But the unintended consequence was I've got people saying, 'Great, the largest market in the world for this is not a market for this because no one will sell it.'"

Getting law enforcement officials and officers to support the products is one good way to build a market.

Two police officers from Florida came up with a trigger lock for the semi-automatic AR-15 called Gun Guardian. It's a detachable pistol grip that releases, rotates 90 degrees and slides over the trigger.

Rob Harvey says they're already pitching it to police agencies. Harvey is betting that when police adopt a gun product, "everybody is like, 'Oh I got to have that product,' then it spreads and I think the public trusts it more."

Mayors launch their own campaign

The campaign to get police interested in gun safety technology doesn't end with endorsements from police. Mayors like Wade Kapszukiewicz of Toledo, Ohio, have signed on.

Kapszukiewicz says Toledo spends about $200,000 per year on guns and ammunition. He plans to use that buying power to pressure companies to start making guns safer.

"This is not legislation," Kapszukiewicz said during an interview in Toledo. "This is not government regulation."

Kapszukiewicz said his city's spending wouldn't change much in this $17-billion-a-year business. But he's working to enlist other cities through the U.S. Conference of Mayors. That could add up to millions.

"If the cities of this country and the mayors of this country band together and create that demand," Kapszukiewicz said, "then maybe a company that doesn't exist right now or a division of a company that doesn't exist right now, could."

Guns & America is a public media reporting project on the role of guns in American life.