As we can see from this webpage, if both watches are looking at the same conversation, they can freely communicate with each other via taps, heartbeat and sketches. I'm really wondering how that Digital Touch feature could happen if the people you want to communicate with do not have the relative app open. If I open up Digital Touch and I want to communicate with a friend but he has his Watch locked for instance, will he receive a notification of some kind? If I've sent to him 10 sketches in a row, will he receive them one by one as soon as he opens Digital Touch app? I really can't see how that could work if both users do not have the app open. I believe that a notification that says "Hey, your friend Steve just tapped on your wrist!" would be very silly. Any thoughts on how that could work? Probably even Apple doesn't know