Actually I'm checking paladin abilities, and you do need to focus it as a move action.  It's at-will, so you never "run out" of uses, but it's also not automatic.<br/><br/>Specific rules: http://www.d20pfsrd.com/classes/core-classes/paladin#TOC-Detect-Evil-Sp- (http://www.d20pfsrd.com/classes/core-classes/paladin#TOC-Detect-Evil-Sp-)