A key thing to remember about traps: perception merely tells you that something is there, not anything about it. That is what investigation is for, and a poor roll on that could easily set off the trap.
That point aside, perception should be used to reveal things like "you notice a scuff mark along the floors and ceiling next to the wall, some discoloration in a pattern, a thin wire running across the hallway, a floor tile that appears to be a pressure switch of some kind, or a groove in the wall/floor. It is up to the players to decide if such descriptions mean a trap and precisely what that means as a trap. Scuff marks on the floor in ceiling could be a secret door or early some sort of crushing wall trap, a thin wire may actually be the key to opening a secret door or it could release a falling boulder, a floor tile may shoot a puff of poisonous gas, or it may just light the next room or could even be a meaningless switch (or broken trap).
Want to mess with them? Put an obvious chest at the end of a hallway filled with traps. Make the chest locked, but untrapped and empty. If you REALLY want to mess with them, make the traps self-resetting so they have to go back through them again.
The point is to play with player expectations. Give them descriptions and find ways to not be consistent or simple with your traps. Maybe the trip wire helps to hide a floor switch behind it (thus a higher DC to perceive)? And remember to use every sense. An electric floor tile may not have anything visual, but maybe they can hear an electric hum, or feel the hair on their skin rise statically as they near it. Traps need not be impossible merely serve as obstacles to slow or deter players.