The problem is that something as ambiguous as you described requires human-level AI. But if you could accept portions of it, you could build a detector for unu

The problem is that something as ambiguous as you described requires human-level AI. But if you could accept portions of it, you could build a detector for unusual vehicles (would yield a lot of false alarms). And a detector for beautiful sunsets. A system that would recognize individuals by gait and be trained by you for specific authorized persons. A detector for water on the ground. It's possible to just detect any movement or significant change in the scene, but that would yield quite a few events that were actually not interesting. Like birds landing.