Hot Cars Act of 2019 This bill requires the Department of Transportation (DOT) to issue a final rule requiring all new passenger motor vehicles weighing 10,000 pounds or less to be equipped with an alert system to detect the presence of an occupant (e.g., a child or domestic animal) in a rear designated seating position after the vehicle engine is turned off. DOT must also consider requiring systems that can detect the presence of any occupant unable to independently exit the vehicle and the presence of a child who has entered an unoccupied vehicle independently. The alert must (1) include a distinct auditory and visual alert to notify individuals inside and outside of the vehicle of the presence of an occupant which must be combined with an interior haptic warning (i.e., vibrations), and (2) be activated when the vehicle engine is turned off and the presence of an occupant is detected. DOT must enter into an agreement with an independent third party for a study on retrofitting existing passenger motor vehicles with technology to address the problem of occupants left unattended in motor vehicles.