I read about the recent ambush and shooting of two New York police officers as they sat in their patrol car. The attacker apparently approached from the rear and finally shot them from the side of the vehicle.
I recall Ford Motor was offering a 'police surveillance package' that alerts officers if someone apparently approaches from the rear, or at least allows them visibility. I know it's too late for those New York officers, but hopefully more patrol cars can consider this option.
http://www.leftlanenews.com/ford-to-expand-police-interceptor-surveillance-mode-to-other-models-video.html