At speeds above approximately 20 mph, this system can alert the driver to some unseen vehicles in the next lane. If radar sensors in the rear bumper detect a vehicle in the "blind spot" area to either side, an indicator lights up in the appropriate side mirror. If you activate a turn signal while a vehicle is detected, a warning sounds. And if you disregard the alerts and begin changing lanes, advanced active technology can apply the brake to a single rear wheel, to help guide the car back into its lane.