An alert system for a vehicle is provided for alerting an occupant of the vehicle that a pedestrian or bicyclist is approaching the vehicle and may collide with a vehicle door if the door is opened. The alert system includes a mobile communication device carried by a pedestrian or bicyclist and operable to communicate information regarding location and motion of the mobile communication device. A receiver is at the vehicle and receives a communication from the mobile communication device. A processor processes information communicated in the communication. The processor, responsive to processing communicated information, determines whether or not the location and motion of the mobile communication device relative to the vehicle is indicative of a hazardous condition. The alert system, responsive to the processor determining that there is a potential hazardous condition, generates an alert to the occupant of the vehicle.