I'm assuming you're writing an app, can detect this state, and want to trigger a rule when you know it's the case. If not but it's similar, the following options will probably still work. 
I see two possibilities. You said "easy," and in that case, a switch device that your app turns on or off or maybe a presence device you set present/not present (or really any stock or custom attribute with the appropriate rule trigger) would probably be easiest. But for a more sophisticated approach, you could instead invoke the Rule Machine API.