The Blind Spot Detection System detects traffic situations that could pose a risk if the driver changes lanes. Such traffic situations include vehicles approaching quickly from behind or vehicles in the driver's blind spot. An illuminated triangular warning LED appears in the exterior mirror if there is a vehicle in this critical area. Looking for a quick answer? Check out our FAQ page : faq.bmwusa.com Need further help? Contact us here: bmwusa.com/contact-us.html You can also refer to your owner's manual or visit: bmwusa.com/owners-manuals.html Connect with BMW USA: Website: bmwusa.com Facebook: facebook.com/BMWUSA Twitter: twitter.com/BMWUSA Instagram: instagram.com/BMWUSA Tumblr: BMWUSA.tumblr.com