I am from Poland, so sorry for my english :x
It always seemed strange to me when police cars going in my direction with disabled siren and enable it only when they get very close if have more than 1 star. I decided to change it. This is my first script, so I don't promise that works perfect. Let us be of good cheer :3
Effect was presented in film.

Update:
Fixed enablind siren in police car, which you driving. It was my oversight.