Voice technology gadgets, including Amazon‘s Alexa and Google‘s Duplex, could get caught up in the next data protection battleground.

The implementation of new data rules in Europe, coupled with increased consumer awareness following the Facebook and Cambridge Analytica scandal, is helping to bring voice data privacy into the spotlight.

Google recently made headlines when CEO Sundar Pichai demonstrated its latest development in voice — its Duplex AI system was used to book a hair appointment and a restaurant reservation. While it sounded natural, it was a conversation between a computer and a real business. Google has since clarified that it will make sure to let people know whenever it’s the automated machine calling and not an actual person.

The Duplex system is capable of carrying out complex conversations without any human involvement, and while that excites many people, some are concerned about the ramifications on privacy and the knock-on effects to the future of advertising.

Should the person on the other end of the phone be made aware they are speaking to a machine?

Peter Cahill is a leading expert on voice technology and is currently the CEO of voice-AI platform Voysis, he says the recent Duplex demonstration shows how far Google is ahead of other voice competitors and has made people realize that voice has moved well beyond just using a smart home speaker to stream your music.

“It puts pressure on other assistants to raise their game but also raises ethical questions for the person at the other end of the line. Google is collecting their data and using it without them giving consent at any point. If you ask Google for help, a recording of your voice is stored in the cloud. But, more interestingly, that recording also contains rich layers of sounds that tell us a lot about you and your environment,” he said in an email to CNBC.

Google says that, similar to your search history, your Google Assistant history can be viewed at any time and deleted by the user. A Google spokesperson reiterated to CNBC via email that “transparency in the technology is important” for the company and it is designing Duplex with “disclosure built-in.”

Citibank recently announced an integration with Apple’s Siri, which allows customers to use their voice to navigate through their account. Alice Milligan, Citi’s chief digital client experience officer, said on the release of the bank’s second annual mobile banking study that “We think that’s the way people are going to interact; it’s the next generation of navigation. And it helps eliminate things that are not easy to find and have therefore been a friction point.”

J.P. Morgan Chase and Marriott Hotels are just two other big firms that have added voice technology to various parts of their customer interaction. The feeling among many experts is that people do want these vast improvements in machine and computer interaction, but that they would always like to know they are interacting with a computer.

The extension of voice technology to advertising is of chief concern among critics. Google has long committed to complying with data regulation and research has shown the recent implementation of the General Data Protection Regulation (GDPR) in Europe has actually helped Google’s advertising business. Google says it will continue to enhance transparency on data use for users and has updated its account creation to allow users more options on data use.

Cahill outlined new scenarios for advertising that included brands using your profile to figure out which media commentator you trust and serving an advertisement in their particular voice.

“A profile that is created from the things that you say, that knows the brands you interact with and in what context, can be extremely dangerous — especially if you can’t tell the difference between a sponsored message and an authentic endorsement.” he told CNBC in an email.

Analysis firm Juniper Research shows smart speakers will be installed in 55 percent of U.S. households within the next four years, and that total advertising spend on voice will reach $19 billion in the same period. The fast developments have led experts, consumers and lawmakers alike to one conclusion — we need to talk about voice.