adb devices was working fine last year, but after upgrades and new software installs,
adb devices no longer recognizes USB attached Android devices.
Her
This thread is old but perhaps my answer will help somebody. Using a Motorola MB865 with OSX, ADB would recognize my phone only after I performed a factory reset.
I got the idea from this thread.
This was after I tried all the other tricks listed in other threads:
adb kill-server followed by adb start-server
Make sure USB Debugging is enabled
Make sure vendor USB ID listed in adb_usb.ini
Switching USB cables. For what it's worth, I did have to switch cables in order for the Mac to see the device. But this had no effect on ADB.
In the end, the factory reset did the trick.