Detect Illusion

You are able to identify illusions within range. In the first round, you become aware of the presence or absence of illusions. In the second round, you determine the number of illusions. In the third round, you learn the location of each illusion. For the duration of this spell, you have tactical advantage on saving throws against illusions. 

The spell can penetrate most barriers, but it is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt.