I have the latest version of Android Studio and an Android device.
I turned on developer mode on my device and plugged it to my lap top via USB.
I didn't get the prompt message that asks me to authorize USB debugging with this pc and also my device list was empty when I ran on the cmd adb devices.
I tried to do adb kill-server and then adb start-server but the devices list was still empty and I still didn't got any authorize usb debugging message on my phone.
I tried to restart phone + PC + change USB cable but nothing.
This helped me at the end:
Quick guide:
Download Google USB Driver
Connect your device with Android Debugging enabled to your PC
Open Device Manager of Windows from System Properties.
Your device should appear under Other devices listed as something like
Android ADB Interface or 'Android Phone' or similar. Right-click that and
click on Update Driver Software...
Select Browse my computer for driver software
Select Let me pick from a list of device drivers on my computer
Double-click Show all devices
Press the Have disk button
Browse and navigate to [wherever your SDK has been installed]\google-usb_driver and select android_winusb.inf
Select Android ADB Interface from the list of device types.
Press the Yes button
Press the Install button
Press the Close button
Now you've got the ADB driver set up correctly. Reconnect your device if it doesn't recognize it already.
Source: Stackoverflow.com