Unlike other carmakers, Tesla Motors doesn't introduce updates at model-year intervals.
Instead, it adds new features into production cars as soon as they're ready, meaning sometimes customers get a bit of a surprise.
That's the case with two new features--lane-departure warning and "speed assist"--that have been added to the Model S electric car recently, without any formal announcement from Tesla.
The photos appears to indicate that the speed-assist system warns drivers if they are exceeding posted speed limits.
It uses a camera mounted on the windshield behind the rear-view mirror, along with GPS data, to determine the local speed limit.
The camera also allows the system to read road signs, which are compared to GPS data to determine the speed limit.
In the absence of signs, GPS data alone is used. Drivers can also set an arbitrary speed limit.
The speed limit is displayed as a gray line on the car's speedometer. If the limit is exceeded, the system can warn the driver--either by displaying the excess speed in gray, or with an audible chime.
The lane-departure warning feature functions like those currently available in many other cars: The same windshield-mounted camera monitors lane markers, and control logic detects when the car starts to pass over them without the driver signaling or turning the steering wheel..
The system then vibrates the wheel to alert the driver, though only at speeds above 30 mph.
Both of these features will help the Model S compete against other luxury cars in its price range, which offer comparable driver-assistance features and much more.
The appearance of speed assist and lane-departure warning closely follows the launch of version 6.0 of the Model S operating system, which includes features like remote start and location-based programming for the air suspension.
However, the new driver-assistance features require extra hardware as well as software, so they likely can't be retrofitted to existing cars.