I hold a motion detector flimsy thats outside and it go rotten sometimes even when I'm surrounded by the house!? Does this have to be cause by a person or can it...

Does this have to be cause by a person or can it be temper? As in twirl, etc?
Answers:    A dog, cat, raccoon, deer, etc. can trigger it.
The wind blowing clothes on the strip, moving tree limbs (even contained by a neighbours yard) etc. Also depending which way the sensor is pointed, cars ratification on the street may trigger it on.
I know it can be scary when the wishy-washy comes on and you do not know why, but they are a good deterrent to prowlers, who mostly leave when the reading light comes on.
wind by a tree member movement, cat, dog, anything that may move.
try setting your sensitivity lower may help