Blind Spot Information System (BSI) Radar Units
WARNING: This page is about a different car, the 2013 Acura MDX, 2012 Acura MDX, 2011 Acura MDX, and 2010 Acura MDX. However, it is still accessible from the selected car via links, so may be relevant.
The BSI radar units are installed in the rear bumper on both sides of the vehicle. They detect other vehicles as they approach your vehicle from the rear sides, and they send this information to the BSI control unit.