Discern lies

Discern lies, also known as detect lie, was a divination spell that revealed deliberate falsehoods. It was one of the spells available from the Balance of Belaros, a holy relic of Tyr.

"Always wield the sword of truth, for it is the keenest weapon."

- Halruaan saying

Effects
After casting this spell, the caster could concentrate on a target creature and know if it was deliberately speaking falsehoods (unless the target resisted the spell). The caster had to be in range (30 ft or 9.1 m for beginning casters) for the spell to operate. The caster could switch targets every so often, until the spell expired, but all targets had to be within range. No truth was revealed by this spell, only the fact that the subject willfully prevaricated while the caster concentrated on that subject.

The reversed form, undetectable lie, protected against magical detection of lies spoken by the target creature for 24 hours.

Components
The newer version of this spell only required verbal and Somatic components and the priest's holy symbol The older version also required a small handful (one gold piece worth) of gold dust. Undetectable lie required the equivalent amount of brass dust.