- Level of awareness: Unattentive (If you're completely not paying attention, like reading a book or watching TV, -1) vs generally attentive (such as a guard on patrol but not specifically aware of a threat/a policeman generally searching a crime scene but not looking for any specific piece of evidence, no bonus or penalty) vs highly attentive (the same guard now specifically searching for an intruder - either seen, heard or responding to an alarm - or the same cop now specifically searching for a particular piece of evidence like a gun or fingerprint they know should be there - +1 or +2)
- Intoxicated (alcohol, drugs or some kind of potion); -1 to -3
- Fatigued or bored: -1, like a security guard coming to the end of his shift
- Exhausted: This isn't just "end of shift" fatigue or boredom, this is the character/NPC who's slept 3 hours in the past 30. -4 to Perception
- Fresh and alert: the same guard just coming on shift, +1
- Afraid. Anything from +1 (for minor anxiety keeping the character on his toes and his ears pricked) to -3 or -4 (for a character so scared out of his mind he's likely to miss the blindingly obvious).
- Darkness - obviously something that will only affect sight-based perception checks, for characters without Night Vision. I feel like this should be pretty high, but would -5 be too much?
I'll undoubtedly come up with more penalties and bonuses over time, but I'd appreciate any other suggestions to expand the list.