Google Home no longer needs to rely on thermostats and other smart home devices to know if you're home. The system can now use Nest speakers and smart displays to detect your presence.
For example, if you talk to Nest Audio or click on the Nest Hub, Google will “guess” to turn on the lights. The second-generation Nest Hubs can also use their Soli radar sensor to detect if you are nearby.
You can turn on presence detection in the Google Home app for Android and iOS under Features in settings.
Until now, Google Home has been able to understand that you're home using data from Nest Guard, Nest Protect, Nest Thermostat or the Nest x Yale smart lock in tandem with the location of your phone. The problem is that this data is far from accurate: you could, for example, lock the door when someone is still home. Using speakers and displays can make Google's smart home system more reliable, especially in non-standard situations.