Indeed, Alexa and Echo — the cylinder-shaped speaker that comes pre-loaded with Alexa — appear to be sleeper hit for Amazon, with sales of more than 5 million as of this November, according to Consumer Intelligence Research Partners.

Prior to this year’s CES, Alexa was already impressive. Using natural language, you could call up your favorite radio stations, ask for news summaries, reorder deodorant, start cooking timers, and so on.

If Alexa were simply a voice-controlled speaker, it would already be an unqualified success. (Again, look at the estimates.) But the technology’s real impact has turned out to come from its ability to be updated with new so-called “skills” that come from outside parties. As is often the case with Amazon, the company had the foresight to open up access to Alexa so other companies could develop functions that play nice with their own products or services. A risky business move, to be sure, but one that has seemingly turned out to be extremely savvy.

Early on, Alexa’s abilities were somewhat limited, if amusing: the ability to answer random trivia questions, for example. But once Alexa could control other devices such as Philips Hue bulbs and the Nest Thermostat, the virtual assistant became much more useful. Other companies caught on quickly that Alexa’s voice-control capabilities and, crucially, the ease of creating skills for her, turned out to fill a gap in their own products, and in the past year, Amazon’s once modest but successful wireless speaker has arguably become the most powerful presence in the consumer-facing smart-home space.

What’s less clear is where things go from here. The so-called “smart home” space is already crowded with other companies vying for consumer dollars. Apple’s (Alexa