The detect evil spell discovers emanations of evil from any creature, object, or area. Personal alignment, however, is revealed only under unusual circumstances: persons who are strongly aligned, who do not stray from their faith, and who are powerful might radiate good or evil if intent upon appropriate actions. Powerful monsters send forth emanations of evil. Aligned undead radiate evil, for it is this power and negative force that enable them to continue existing. An evilly cursed object radiates evil, but a hidden trap does not.
The degree of evil (dim, faint, moderate, strong, or overwhelming) and possibly its general nature (expectant, malignant, gloating, etc.) can be noted. If the evil is overwhelming, the caster may be able to detect its general bent (lawful, neutral, or chaotic). The spell has a path of detection 10 feet wide in the direction the caster is facing. The caster must concentrate for at least one minute to receive a reading.
There is also a reversed version of this spell, detect good.
Note: This version of detect evil originally appeared in the 2nd Edition Player's Handbook for Advanced Dungeons & Dragons from TSR. Its use here is for the purposes of providing context for the campaign only.