Google parent Alphabet Inc. (NASDAQ:GOOG)(NASDAQ:GOOGL) just capped a banner year, with shares climbing by nearly a third in 2017 -- and for good reason. The internet search giant's quarterly results repeatedly crushed Wall Street's expectations, largely as the outperformance of its mobile and YouTube platforms drove impressive growth for its core advertising business.

But that's not the only reason you might still want to buy Alphabet stock today. Consider that revenue from Google's non-advertising products also climbed 40% year over year last quarter, to over $3.4 billion, with broad growth from its cloud products, Google Play, and sales of hardware devices such as Chromecast, its Pixel smartphones, and the Google Home line of smart speakers.

Of course, that's a small slice of Alphabet's total revenue of nearly $27.8 billion last quarter. But you'll be hard-pressed to find an investor willing to complain about a separate fast-growing source of revenue from a multibillion-dollar base. 

400 million and growing

The driving force underlying Google's slick hardware lies something even more important, and something that should make Google's platform even more pervasive: the Google Assistant.

According to a blog post from Google on Friday, Google Assistant is now available in eight languages on more than 400 million devices and growing -- a remarkable feat, considering Google only just unveiled the cutting-edge virtual personal assistant at its developer conference in mid-2016.

Google home smart speakers on a white table with grey background

GOOGLE HOME DEVICES, IMAGE SOURCE: ALPHABET.

Bigger, smarter, faster

The launch of Google Assistant marked a significant expansion over the company's more limited "OK Google" functionality, notably adding capabilities like holding and understanding two-way conversations, and presenting personalized results depending on who is talking. Google Assistant is also able to handle voice commands for over 1,500 smart-home products from 225 manufacturers, as well as perform an array of tasks from listening to music, ordering food, handling meetings and appointments, or simply asking any question you might otherwise want to type into a traditional Web search.

Of course, those 400 million devices don't just include Google-branded hardware. Google Assistant can also be found on all Android phones and tablets, iPhones, TVs, vehicles, and virtually any other internet-connected, app-enabled wearable technology like smartwatches and headphones.

Even so, Google says it has sold "tens of millions" of its own Home devices over the past year, including more than one Google Home device every second since it started shipping Google Home Mini on October 19, 2017. Put another way, simple arithmetic tells us that Google has sold more than 6.7 million Google Home devices over that short span.

If Google wasn't already everywhere...

Perhaps it should be unsurprising, then, that Google Home usage climbed ninefold this holiday season compared with the same year-ago period.

As such, it seems the astronomical rise of Google Assistant is serving as an effective medium to not only drive sales for Google's lucrative non-advertising revenue stream, but also to add to its treasure trove of valuable consumer data while making its platform an even more ubiquitous part of our lives.

In the end, assuming Google Assistant can sustain this momentum in the coming quarters, we can chalk it up as yet another reason to buy Google Stock today even after last year's enviable gains.  

Suzanne Frey, an executive at Alphabet, is a member of The Motley Fool's board of directors. Steve Symington has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Alphabet (A shares) and Alphabet (C shares). The Motley Fool has a disclosure policy.