Unity and Vuforia

Hello guys, I need some help with Vuforia (Augmented Reality)for Unity
Do you guys know or have any idea, how can I detect the device’s camera that Im pointing to with my app that is installed on my device which I am holding.

I know how to trigger over a paper(or some object that I have with the same texture or trigger points ) but I dont know how to make it to detect another phone(device), since for example 2 unknown people from somewhere around the world will download it and will try to play.

So, imagine, you are staying in a room with a friend and each one with a phone and with this app, so at some point if you will face your phone (or lets say record ) the other phone, somehow the app will trigger (detect) your friend’s phone.
Any advice will be appreciated
I hope you will understand, if not please replay.

Unless the camera/phone has some distinct features, I don’t think you can do it directly. Alternately you can upload phone2’s GPS coordinates, facing direction… to your server, then every other phone (include phone1) will polls information about phones that maybe close to them, then render it back. That’s the way Metaio do it.