The move is said to be a way to ward off competition from Amazon, and it comes four years after Google bought Nest for $3.2 billion (£2.3 billion) and created Alphabet as part of a major restructuring.
After two years of operating as a standalone firm, the subsidiary - which has created devices including an app-connected thermostat and a video doorbell - will be combined with Google's own team once again.
In a statement, Alphabet said: "[The goal is] to supercharge Nest's mission: to create a more thoughtful home, one that takes care of the people inside it and the world around it...
"By working together, we'll continue to combine hardware, software and services to create a home that's safer, friendlier to the environment, smarter and even helps you save money--built with Google's artificial intelligence and the Assistant at the core."
The company's rival Amazon is providing increasingly heated competition - after launching its own home security device - while its Echo devices are an equivalent of the Google Home products.
It follows Google making a move over the past few years to focus on creating home products, included the Pixel electronics line and the Google Home speakers.
Just last week, it was announced that Alphabet's Google unit had paid $1.1 billion for a sizable amount of HTC's hardware operations, which resulted in it gaining roughly 2,000 engineers in Asia.