Voice assistants like Apple's (NASDAQ:AAPL) Siri, Alphabet's (NASDAQ:GOOG) (NASDAQ:GOOGL) Google Assistant, and Amazon's (NASDAQ:AMZN) Alexa have integrated themselves into our digital lives. Almost half of American adults used voice assistants last year, according to Pew Research.

Earlier this year, PwC reported that U.S. internet users who spoke to their devices interacted with smartphones most frequently. However, users are also talking to their tablets, PCs, and smart speakers.

Devices which U.S. internet users have given voice commands to.

Data source: PwC. Chart by author.

PwC's survey didn't break down those devices by individual operating systems. However, Voicebot.ai recently found that Siri controlled 45.6% of the voice assistant market, although iOS and macOS devices account for much smaller slices of the mobile and desktop markets, respectively, than Android and Windows. Google Assistant claimed 28.7% of that market, while Amazon's Alexa ranked third with a 13.2% share.

Looking ahead, the smart speaker market could grow at a whopping CAGR of 34.4% between 2018 and 2023, according to Research and Markets. That would make the market, which Amazon dominates with its Echo speakers and Alexa devices, the next big battleground for voice assistants beyond mobile devices and PCs.

John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Leo Sun owns shares of Amazon and Apple. The Motley Fool owns shares of and recommends Alphabet (A shares), Alphabet (C shares), Amazon, and Apple. The Motley Fool has the following options: long January 2020 $150 calls on Apple and short January 2020 $155 calls on Apple. The Motley Fool has a disclosure policy.