From Pathfinder Society Scenario #4-09: Killer in the Golden Mask, which isn't enabled.

Greater Fireball Rune

HAZARD 7

Stealth +17 (expert)

Description An invisible rune creates an invisible, spherical magical sensor with a 20-foot radius.

Disable DC 25 Thievery (expert) to erase the rune without triggering the sensor, or Dispel Magic (4th rank; counteract DC 23) to counteract the rune

Fireball (arcane, fire)

Trigger A living creature enters the sensor area

Effect The rune detonates a fireball centered on the triggering creature's square. This is a 4th-rank Fireball spell that deals 8d6 fire damage (DC 25 basic Reflex).

Pathfinder Society Scenario #4-09: Killer in the Golden MaskOGL