So when Unity 5.1 came out a couple of days ago I figured I would do a clean install and go ahead and get it set up for Google Cardboard. While Unity 5.1 includes some New Virtual Reality features, native cardboard support isn’t one of them, so off to the Google Cardboard site to get the SDK for Unity on Android. Installation is pretty straight forward overall, just don’t be in a huge hurry as the Android SDK step took well over an hour by itself. Everything was going great right up to the final Build and Run step and Unity couldn’t find my phone. (Moto X with Android 4.4.4)
So after some digging around I found I had a couple of issues, I needed to Enable USB debugging and update my USB drivers specifically for the phone.
First to enable USB debugging, you need to get your phone into developer mode and just to make things interesting the function is totally hidden. You need to select, Settings > About Phone > scroll down to the bottom and tap Build number seven times.
This will add a Developer options section to the Settings menu, check off USB debugging with your phone connected via USB and Check Always allow from this computer when the Allow USB debugging prompt comes up. This is the procedure for Android KitKat and Jelly Bean. If you have an older phone the developer menu isn’t hidden and USB debugging can be found either right on the Settings menu or Settings > Applications.
Needing to update my USB drivers may only be a specific issue to my particular phone or setup. If you have a motorola phone with this issue get the Motorola Device Manager for Windows or Mac that has the updated USB drivers. After the USB updates and a reboot Build and Run worked just fine. Hopefully this will save you some frustration and searching around if you have the same issues. Good luck!