It's been possible to dictate Nest products for some time now, though you'd need to be fairly savvy at linking multiple home automation systems and setting up recipes within IF (né IFTTT). Today, Nest is making life much easier by introducing Family Accounts and a native Home/Away Assist function.
In a nutshell, the Nest app update now allows you to select up to 10 people as family, and if any one of them are home, your Nest Thermostat, Smoke + CO Alarm, and Camera will operate accordingly. Once the entire crew heads out, the system will automatically do what's necessary to save energy. Notably, Nest's engineering team is using more than a typical geofencing system to determine who is in and who is out -- it'll tap "learning algorithms and activity sensors built into Nest products" in a bid to be more accurate.
Since you're wondering (and because Nest is owned by Google), the company has proactively announced that the Home/Away Assist function doesn't track where you go; rather, it only takes note of whether you're at home or away from it.
Of course, as brilliant as all of this sounds, the state of home automation is still a disaster. Nest only makes three products, and forcing your non-Nest leak, door, window, humidity, and motion sensors to operate on the same cadence remains a headache. Unless you're up for the challenge of getting disparate systems to speak a common language across varying protocols, you may still be better off doing things the old fashioned way.