Aerial Alarm

(Heroes of Battle)

Level: Ranger 2, Sorcerer 2, Wizard 2,
Components: V, S, AF, DF,
Casting Time: 1 standard action
Range: Medium (100 ft. + 10 ft./level)
Area: 100-ft.-radius cylinder, 500 ft. high
Duration: 2 hours/level (D)
Saving Throw: None
Spell Resistance: No

As alarm (see Player's Handbook page 197), except the area is a cylinder that extends 500 feet into the air and the alarm only sounds when a flying creature of Medium or larger size enters or touches the warded area.
Arcane Focus: A silver bell and an eagle's feather.