Zone of truth

Zone of truth was an enchantment spell that prevented lies from being spoken within the area of effect.

Effects
For a few minutes, an area designated by the caster became a no-lie zone. Creatures within the area knew they were being compelled not to speak falsehoods, and could resist the spell, but those who could not resist could not lie for the duration of the spell. Note that affected creatures were not compelled to tell the truth; they could remain silent or evade questions as long as they were truthful.

The area of effect was either a square with sides as big as 5 ft (1.5 m) per level of the caster, or a 20 ft (6.1 m) radius sphere, depending on which version was being cast.

Components
In addition to verbal and somatic components, and the priest's holy symbol or divine focus, the older version of this spell required a cheap imitation emerald, ruby, or diamond to cast.