Feeling that one should not be penalized for actively doing something, we decided that an active Perception check should always be higher than a passive one. To accomplish this, we simply roll a d10 and add it to the passive Perception score. I know this breaks with the whole d20 idea, but it feels more natural.
The other rule we have tried is to roll an Endurance check (DC: 10) before camping each night. If the check succeeds, then the player can make an active Perception check to obtain a score for his or her watch. If the Endurance check fails, then the player uses his or her passive Perception score. A failed check represents the character becoming distracted or inattentive.
The other rule we have tried is to roll an Endurance check (DC: 10) before camping each night. If the check succeeds, then the player can make an active Perception check to obtain a score for his or her watch. If the Endurance check fails, then the player uses his or her passive Perception score. A failed check represents the character becoming distracted or inattentive.