Following a recent refresh with Material Design, iPhone 6 support and Maps in search results, Google's main search client for iOS and Android today gained the ability to interact with your Nest smart thermostat, along with other Nest-branded devices for the connected home, using Google Now voice commands.
Replicating some of the functionality provided by Nest's own iPhone application, Google's native search app for the iPhone and iPad takes advantage of voice input and Now cards to help control your Nest hardware.
Just fire up the app and either tap the mic or say "Ok Google" to get started. This is a silent feature upgrade on the backend so no download is required.