One-Way Lock

This spell magically locks any one door, chest, or portal upon which it is cast as a wizard lock. However, the closure is locked from one side only (caster's choice) and can be opened freely from the other direction. The door or portal can be opened from the locked side only by breaking it down, using a knock or dispel magic, or by a wizard four or more levels higher than the caster. If the one-way lock is bypassed by a knock or a higher-level wizard, it is negated only temporarily and remains in force.

Notes: Uncommon spell. (Updated from Polyhedron Magazine.)