According to the Motor Trend blog, the aptly yet simply named "Blind Spot Detection" system uses radar which scans the area commonly referred to as the driver's "blind spot" around the vehicle. When it senses an object, it alerts the driver. The system is similar to the one used by by rival Volvo. The companies Raytheon and Valeo co-developed it.
More details can be found above. Our take? While not quite as showing as GPS or car entertainment systems, we feel such a system is more important. This is especially true as a vehicle's B-pillar, the support between the car's A and C-pillar's greenhouse, grows thicker to house airbags. The increased safety makes it more difficult to see anything in the blindspot.