Beta software update activates autopilot mode in newer Tesla cars. The system does not recognize stop signs or red lights, so it's not 100%.

Tesla Software Update Adds Autopilot | News & Opinion | PCMag.com

Every car manufactured by Tesla as of late September 2014 will support Autopilot. Those vehicles have a special system of four sensors: ultrasonic sensors (below) around the perimeter of the car that can detect obstacles; a forward-facing camera with image recognition that sees lane markings and signs; forward radar that can detect large objects and navigate through bad weather; and GPS with high-precision maps for navigation.