The beauty of computers… do it once, and you can do it every time. So it won’t be cumbersome. If you’re thinking computional wise… Put in a delay and test every 0.5 seconds instead of tick.
And the system I described won’t have to be binary.
If you have 3 point you detect to, you can weight each point. Head 20%, Torso 50% and legs 30% for example.
Couple this with distance… 100 units away vs 250 units away vs 500 units away. Different distance, different visibility.
This would create a pretty Thief like system and feel I am almost certain.
If you on top of this add something that takes your speed into account it would be very very detailed actually.