Three years ago, U.S. Bank tested a virtual assistant within its mobile app. Customers could search their transactions and pay bills using their voice. The bank decided to forgo any rollout after the test because of reliability issues — the system sometimes returned false or irrelevant information when it failed to understand a request, said Dominic Venturo, U.S. Bank's chief innovation officer.

Today, reliability is much better with voice recognition technology, as Apple, Google, Amazon and Microsoft are all investing heavily in their Siri, Google Assistant, Alexa and Cortana voice-based assistants. Banks are grappling with new challenges in trying to work with these voice assistants and securing transactions conducted through them. Some are debating whether to work with them at all.

"We still must be thoughtful about what data will be passed into these third-party systems," Venturo said. "Right now we have to evaluate these one by one."

Such challenges mean that 2017 won't be the year that voice banking takes off. Significant customer adoption of voice banking is three to five years away, said Emmett Higdon, director of mobile for Javelin Strategy & Research.

Still, banks can't afford to stall their efforts around voice, given growing consumer use of the technology in everyday situations. Consumers will be using voice assistants across an increasingly varied array of devices: on smartphones, in connected cars, on wearable devices and on smart home devices like Amazon's Echo, the new Google Home or Apple's rumored Echo competitor. A recent Citigroup survey of general consumers with bank accounts found that 74% of the respondents were already using voice functionality to check weather, send messages and get directions.

Growing adoption of voice assistants with these new types of devices will drive banks to explore new customer experiences that leverage touch, voice and other interfaces.

Most major banks have rolled out some voice capabilities in their mobile apps, such as allowing customers to log in via a spoken phrase or password. The next important step for voice banking will be bringing voice assistants to mobile banking apps, Higdon said.

In a Javelin survey this summer, half of the respondents — in this case, consumers who have used mobile banking — said they would be interested in using voice control within their mobile banking apps.

"The problem is on the supply side — banks are not wading in," Higdon said.

However, more banks will be experimenting in the coming year with developing their own voice assistants, he said.

Bank of America announced in October that it planned to roll out Erica in 2017. The virtual assistant will be available within its mobile app and, when activated by a customer, will use artificial intelligence to offer basic financial advice via voice or text message. The bank has said that it wants to use Erica to bring some of the one-on-one personal service and advice normally reserved for its premier clients to the rest of its customers.

Other banks will follow suit, with most likely to partner with companies like Nuance, Kasisto and Personetics that specialize in providing voice assistants, Higdon said. Such technology is a lot mature than when U.S. Bank tested it a few years ago.

But U.S. Bank isn't saying whether it has plans to reconsider voice anytime soon.

As for the step beyond that — letting customers use voice assistants from the tech giants to do banking tasks — banks have been even more hesitant. So far, Capital One is the only major bank that allows customers to check balances and pay bills through Amazon's Echo.

Making payments, checking balances and transferring funds with these systems requires sharing account information through them. The technology underpinning virtual assistants such as Alexa in Amazon's Echo is all exclusively owned and tightly controlled by the tech companies that created them. So banks have to resolve the complex challenge of integrating their own applications with each one of these systems individually, Venturo said.

And though Amazon, for one, encrypts all the data passing through Alexa, bankers like Venturo say an industry standard around tokenizing or encrypting data that passes through such systems would be helpful.

Despite the challenges banks have in working with third-party assistants like Alexa, Carey Kolaja, global chief product officer for the Citi FinTech unit, expects such assistants will play a big role in helping customers make payments and online purchases going forward.

"Not every transaction will be optimal on every device, and an experience that's optimal for one customer might not be optimal for another," she acknowledged.

As an example, Kolaja recounted overhearing a woman at a Starbucks pulling out an iPhone and telling Siri to set a reminder to pay her phone bill. "I do not believe that woman would have been comfortable in a public forum asking Siri to move $1,000 from her account to another person's," she said.

"So we need to build our products and services on a flexible open architecture that allows us to be responsive [to customer preferences]," Kolaja said.

This adoption of voice commands means that customers will intuitively understand the value proposition behind voice banking — it will make routine banking tasks far easier. For example, banks have struggled for years with making their various products and services easy to discover on mobile devices through menu bars and other tools. With voice recognition technology, a simple spoken query could bring up the bank's relevant products and services, said Patrick Kelly, assistant vice president of emerging technologies at USAA. This would eliminate the need for the clunky menu option — classically represented by stacked lines that are often referred to as a "hamburger" — in banking apps altogether.

Voice also could create entirely new customer experiences, Kelly added. For example, customers could conduct banking and shopping transactions using multiple devices simultaneously. A customer could ask their Echo to pull up their investment portfolio on their smart TV, prompt the Echo to make some transactions, and see the impact on their portfolio's balance displayed on the TV screen.

This would be much faster than tapping or swiping on a touchscreen or TV remote to individually find each asset that the customer wants to buy or sell, allowing the customer to get back to their Netflix binge more quickly.

"This is something that we've been thinking about as omnichannel 2.0," Kelly said. "We can already allow a customer to start a transaction in one channel and then finish it in another. That was the first stage. But doing it across multiple devices simultaneously, that's the next step."

USAA happens to be ahead of most of the industry when it comes to voice. Besides allowing customers to log into its app via voice, it also uses Nina, the virtual assistant from Nuance.

As virtual assistants become "smarter" and more context-aware, their conversational capabilities will present new opportunities for delivering financial advice and education. The Swiss bank UBS recently announced a customer pilot using the Echo to answer customers' questions about investments and the economy.

However, banks' initial efforts with voice assistants need to stay grounded in simple, repetitive tasks like checking balances or searching for a transaction, Javelin's Higdon said. This will help acclimate customers to routinely using voice, so they will eventually feel more comfortable doing so for more complex transactions. "It's important to keep it simple and straightforward," Higdon said. "You don't want to throw too much at the consumer too quickly."