Arduino to Unity 3D Communication

I'm working on some interaction between Unity 3D and Arduino. I'm wondering what might be the best way to tackle something like this:
Lets say I want to have various sensors like an LDR send data into Unity 3D and have that data trigger something in Unity 3D when it reaches a certain value but not have it "Buggy" for lack of a better word. Like activate all the time for crazy reasons.
Basically I would like to trigger some random voice response clips if say the ambient lighting fell below a...

Arduino to Unity 3D Communication