It's a radar-based system that detects vehicles travelling in parallel lanes and uses blinking lights in rear-view mirrors to warn when one is in the blind spot. It's very helpful in preventing you from veering into occupied space, along with the attendant horn-honking and name-calling. More advanced intervention systems apply the brakes to nudge the car out of danger.
Some of these new cars are already scheduled for earlier-than-usual facelifts. The rest of them are already overdue.