Since you can use their last key click to determine if they're AFK, idle or active the way many chat/IRC apps work today, is it feasible (assuming they're using

Since you can use their last key click to determine if they're AFK, idle or active the way many chat/IRC apps work today, is it feasible (assuming they're using a smart phone), to use an app to determine if the user is using the phone capacity of that device and relay that via an icon in the chat? That way you're able to use the existing technology to figure out if they're there without needing to visually prying on them.