Movement Speed and Perception
Our normal of perception rules are designed to cover perception for movement at a "normal speed," this is defined as your normal walking speed or your normal vehicle cruising speed considering conditions. Of course moving slower and more carefully allows one to see so much more.
As usual announce the skill and or affinity that you are applying, presumably setting +2 for paranoia. Then move at 1/2 your walking speed to double your total bonus or 1/3 to triple it. Obviously some degree roleplaying should be involved, "I'm suspicious of a demonic threat and using demon and monster lore to watch for anything odd as I walk slowly down the path." Except in rare cases you must use your characters SPD stat, even in a vehicle.
The net effect is that if you are watching for the right kind of trouble the party is very unlikely to be caught by a trap, ambush, or really anything else that they have any suspicion of.