How to fix AVD Manager unable to detect device even though adb commands work on PC? I am trying to connect my Google Nexus 5 so that I can debug my Xamarin code from Visual Studio with it.  

I have downloaded all the drivers and all that. When I type in adb -d devices it finds my phone. I can do all sorts of things with it from there, so the phone is for sure connected to the computer.  

My problem is how do I get the AVD manager to realize that? It just won't find my phone.
The AVD is not in charge for real devices.

There is a Step-by-Step Tutorial from Xamarin for Nexus devices:

http://developer.xamarin.com/guides/android/getting_started/installation/set_up_device_for_development/

http://developer.xamarin.com/guides/android/deployment,_testing,_and_metrics/debugging_with_xamarin_android/

If this won't work, try to stop your Firewall.