The race to win the U.S. smart speaker market is heating up as Google and Apple begin to close in, very slowly, on Amazon's dominance.

Why it matters: Tech companies can expand their data-based ads and commerce businesses dramatically through smart speaker usage. There are also billions of dollars at stake in smart speaker hardware sales.

By the numbers: According to eMarketer’s latest forecast, Amazon's Echo will drop below two-thirds of U.S. smart speaker users for the first time next year.

While Echo will still capture 63.3% of smart speaker users, it's beginning to face more competition from Google Home, which will account for 31.0% of smart speaker users in 2019, as well as smaller players, like Sonos One and Apple HomePod. (Percentages add up to more than 100 because some consumers own more than one company's device.)

Amazon’s share will continue to shrink through 2020, while those of its rivals will grow, eMarketer predicts.

Be smart: New competitors, like Apple's HomePod and Facebook's Portal, are entering the U.S. market this holiday season, which could also begin eating at Amazon's lead.

Amazon's voice technology is getting clobbered outside the U.S., as Google and Chinese companies look to expand their voice footprints internationally.

eMarketer notes that Amazon has managed to maintain its lead up to this point by brokering partnerships in which its voice assistant could be used on other premium speakers, like Sonos. But now other companies, like Google, are doing the same.

Amazon also faced a privacy storm this year after its voice assistant technology, Alexa, accidentally sent out a recording of a couple's conversation.

The big picture: The U.S. is an important market for speaker makers to own because it has the largest smart speaker market in the world (representing 46% share of the global market), and it's still growing.

Roughly 20% of U.S. adults today use smart speakers, per eMarketer. That number is expected to grow to one quarter (26.8%) of the U.S. adult population by the end of next year.

As a result, smart speaker hardware sales in the U.S. are expected to rise from roughly $2.0 billion in 2017 to $3.2 billion this year, up 64%.

And while revenue from ecommerce sales on smart speakers is still relatively small, at roughly $2 billion in the U.S. this year, that number is expected to balloon to up to $40 billion by 2022, as retailers get better at marketing their products for smart speakers.

The bigger picture: Americans are using smart speakers for more functions and owners are starting to put speakers in multiple rooms within houses, which is driving growth.

For example, there are over 70,000 "skills" (or voice tasks) available on Amazon's Alexa voice assistant in the U.S., per Amazon. These tasks range from ordering toothbrushes online to playing singalongs that teach children how to brush their teeth.

At this point, most people use smart speakers to listen to music or podcasts, search for answers to general questions, or get weather and traffic updates.

News consumption on smart speakers isn't picking up in the U.S. much right now, although many news companies are looking for ways to build better audio newscasts for smart speakers.

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