Aon's alert

A large transparent sphere with a radius of 120 ft that seems to faintly glow silver expands form the caster, things are able to pass through this sphere but when they do the caster is instantly alerted to the creatures size, rough shape, and intentions toward the caster if it has any at all. the caster is able to make a DC 12 wisdom saving throw to clarify what the creature is exactly. when cast at higher spell levels the range increases by 30 ft and the wisdom saving throw DC decreases by one per spell level higher than 2nd