Is there a way to get alerted if someone in your alliance getting attacked and you're not?

There is no function to receive a notification if a fellow alliance member is being attacked by another player. If you have troops stationed in their sanctuary as reinforcements and they are targeted, you will be alerted.

The only other time you will get an attack notification is if a rally is created against your fellow alliance member. A message will appear on the screen and quickly disappear. It alerts everyone in the state that war is being declared.