Newbie Project Help: Sense iPhones on wifi network to trigger Nest

Newbie here.

How feasible would it be to have a photon recognize if an iPhone is on the same wifi network, then trigger an ‘Away’, or ‘Not Away’ notification to a Nest, either through IFTTT, or other means. My Nest isn’t in a high traffic area of my home.

Would I need an app on the phone for the photon to recognize, or is there a way for the photon to scan wifi peers?

I want to know what direction I should take while learning the basics to get me to my end goal. Thanks for any suggestions.