trap seer prevents invisible traps from working (not that when stepping on an invisible trap, it will become visible and will start to work if you or your team pokemon steps on it again)
you get the ability trap seer when you reach a certain IQ level
HINT: feed your pokemon lots of gummis in their FRIEND AREA, not in dungeons because feeding them while they're in their areas will give them more boost of IQ and a random status will raise (eg. attack, sp. defense etc.)