Barbarian Class Ability
Trap Sense (Ex): Starting at 3rd level, a barbarian gains a +1 bonus on Reflex saves made to avoid traps and a +1 dodge bonus to AC against attacks made by traps. These bonuses rise by +1 every three barbarian levels thereafter (6th, 9th, 12th, 15th, and 18th level). Trap sense bonuses gained from multiple classes stack.
Source: Player's Handbook