One of the smartest features of the Google Nest Thermostat is its motion detection, which enables your smart home to react to whether or not you're home – for example so it won't heat an empty house. But a brand new update to Google's Nest devices means you can get very similar features without having to have that particular bit of hardware – so if you have or plan to get Google Nest speakers or smart displays you'll have presence detection too.
The Nest devices that know where you are
Presence sensing is handled in different ways by different devices, so for example the Nest Guard has a motion sensor, the Nest Hub (2nd Gen) has a Soli sensor (a miniature radar) while the Next x Yale lock has an optical sensor that can detect whether the bolt is open or closed. But the most interesting devices are the Google Nest speaker and Google Nest display, which can detect whether you're there because of their touch and audio sensors.
Detecting your presence because you talk to or touch a device doesn't sound very radical, but it's important because it can be used to trigger additional features: clearly if you're talking to your Google Nest speaker, you're home and that could then be used to call additional smart home settings such as turning the light on or turning the heating up. It's not so much the sensing that's important here but the fact that it can set off a chain of useful actions.
If you're worried about privacy implications, the feature is strictly opt-in: you can enable the feature or turn it off again in the Google Home app on Android or iOS.