CIWS should be working in v1.9 without active sensors.
I can now confirm that as 1.9.5 CIWS works without any setting and or Active Sensors, they will shoot as soon as a missile is in range.
Hostile missile -- or did you mean CIWS is firing on missiles from neutral powers?
I had an NPR I still set as Neutral in my test game. They fired missiles at me and the CIWS shot them down. I then switched that NPR to hostile.
Overreact much? What is a few missile salvos between friends, friend?