Constant collsion detection, how would i go about this?

So, while i was in bed last night i was thinking about a way to make a circular collision detection script... now i mustve over thought it quite a bit because i was bringing in geometric equations.. but it shouldnt be that hard should it?

"to make more sense"

How can i make collision script. keep firing when the object is standing still or if the object is still moving within the object... like for example if a player is walking around in a cube do something while hes there.....