Imagine you get a call supposedly from your bank. The caller-who shares your Yooper accent from Michigan's Upper Peninsula-warns you that someone is trying to wire a large sum from your account, then requests your PIN to stop the transaction.

Unusual request, sure. Maybe enough to put you on guard. But chances are your guard is lowered by the familiarity of the caller's voice. After all, the person sounds just like you.

That's what the scammer who contacted you is hoping for. They've discovered that AI, drawing on the huge troves of speech available on social media and other online sources, can now produce highly convincing mimicry of local accents from all over the country.

"It's gotten so good," says Neil Kirk, an associate professor of psychology at Abertay University in Dundee, Scotland, "people naturally default to thinking they are hearing a real human."

For a sense of the reach of AI voice technology, consider this: The most popular voice-generating platform, ElevenLabs, says on its website that it offers more than 10,000 voices in its library and can clone a voice readily available on, say, YouTube or TikTok using just a 10-second clip. Platforms like ElevenLabs (which didn't respond to requests for comment) cater to the many legitimate uses for cloned voices, including entertainment and marketing.

Bots get real

The key for scammers is that the more-refined voices AI can now produce are nothing like the bland, robotic voices you might get when you call a customer-service number.

In a recent paper, Kirk evaluated whether Scottish people would classify recorded human and synthetic speech as human or AI. In the first study, 150 online participants in Scotland were asked to listen to human and AI-generated Scottish Standard English or Dundonian Scots, a dialect spoken by about 30% of people living in Dundee, a city of just 150,000 people.

Most listeners assumed both the human and AI voices were human. "They simply didn't expect a machine to sound like them," Kirk says. They were even more likely to be tricked when the AI recited sentences in Dundonian, suggesting that the more particular the accent, the more likely people are to assume the voice is human.

Research by Na Kyong (Kimberly) Hyun, a marketing professor at the University of Cincinnati, shows the effect a familiar voice can have. In a recent paper, Hyun analyzed 14 seasons of "Shark Tank," the television show where entrepreneurs try to convince members of a panel of potential investors to back them. She found that the closer an entrepreneur sounded to one of the panelists, the more likely that panelist was to make a deal. Hyun studied similarity in timbre, or the overall quality of a voice.

A broader experiment cited in Hyun's paper suggests that casting a wide net by mimicking a voice that would sound familiar to the most people in a target population-rather than aiming to mimic a particular accent-could also work for scammers. Hyun analyzed more than 2,000 Kickstarter campaigns and found that the most successful were ones where the spokesperson's voice sounded more like an average voice.

When you hear a voice that sounds like your own, that triggers perceptions of competence, morality and integrity, Hyun says. Your brain "immediately thinks that person is trustworthy, leading to compliance," she says.

Eyes wide open

So, how can consumers protect themselves from this new level of deception?

If we can't trust a familiar voice as proof of legitimacy, we need to go back to questioning the story the voice is telling us, says James Mullen, head of research at cybersecurity company Edgescan. "Does what they're telling me make sense? Does it line up with what I already know about that person or their situation? We can also contact the person separately using a number or method we already know and trust."

If someone calls claiming to be from a bank, hang up and call the bank yourself using the number on your statement or card. Don't give passwords or other sensitive credentials to an unsolicited caller, no matter how authentic the voice sounds. If a relative calls with an emergency request for money, contact that person or another family member through a separate channel.

But it all starts with awareness, because if you don't see the danger in a situation, it doesn't matter how well-versed you are in protecting yourself. Abertay University's Kirk says people need to update their assumptions that local speech isn't something that AI does. In his research, when he told the participants that AI can now authentically reproduce Scottish accents, their tendency to classify the synthetic voices as human was significantly reduced.

As swindlers scale up this scam, we all need to be more vigilant, no matter how we pronounce "caramel" or "aunt."

Write to reports@wsj.com.