Detect undead

Desecrate is a divination spell that reveals undead creatures within 60 feet.

Effect
You can detect the aura that surrounds undead. The amount of information revealed depends on how long you study a particular area or subject:
 * 1st Round: Presence or absence of undead auras.
 * 2nd Round: Number of undead auras in the area and the strength of the strongest undead aura present. If you are of good alignment, the strongest undead aura’s strength is "overwhelming" (see below), and the strength is at least twice your character level, you are stunned for 1 round and the spell ends. While you are stunned, you can't act, you lose any Dexterity bonus to AC, and attackers gain +2 bonuses to attack you.
 * 3rd Round: The strength and location of each aura. If an aura is outside your line of sight, then you discern its direction but not its exact location.

Aura Strength
The strength of the undead aura is determined by the HD of the undead creature.

Length Aura Lingers
How long the aura lingers depends on its original strength:

Note: Each round, you can turn to detect things in a new area. The spell can penetrate barriers, but 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt blocks it.

Arcane Material Component
A bit of earth from a grave.