Nest Labs was founded by Tony Fadell and Matt Rogers, two former Apple executives, and makes internet-connected thermostats and carbon monoxide and smoke detectors.
The thermostats can determine people's behaviour through room temperature and humidity, and light sensors, and can work out whether people are occupying a room or not.
It follows Google's acquisition of military robotics firm Boston Dynamics in December last year, a company founded by a former MIT professor that can make machines that run faster than humans, and of the human-gesture recognition start-up Flutter in October. The BBC's technology editor David Grossman said the latest acquisition "confirms that Google is no longer just a search engine company."
Nest is to continue under the leadership of Fadell with its own distinct brand identity, and the transaction is expected to complete in the next few months.
Larry Page, Google chief executive, said: "Nest's founders have built a tremendous team that we are excited to welcome to the Google family.
"They're already delivering amazing products you can buy right now – thermostats that save energy and smoke/CO alarms that can help keep your family safe. We're excited to bring great experiences to more homes and more countries."