Owners of Tesla Motors [NSDQ:TSLA] Model S and Model X electric vehicles who didn't pony up for the automaker's Autopilot semi-autonomous system can test it out for a month for free.

If they like it, they can add the software—the hardware is already there—for $3,000. The prize for declining it initially? Buyers get to pay $500 more than they would have for a Model S or Model X that left the factory with the system.

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Autopilot is Tesla-speak for the company's high-tech autonomous tech, which allows drivers to lift their hands from the steering wheel in certain driving conditions. A Tesla optioned with the system's software will move on its own thanks to its radar, cameras, and ultrasonic sensors that read road information and relay it to the vehicle's steering and brakes. 

Tesla launched Autopilot about six months ago, and while it isn't fully autonomous in that it can't read traffic lights or make turns, it does at least allow drivers a relatively high degree of hands-off motoring. Similar systems are available in BMW, Mercedes-Benz, Infiniti and other premium brand vehicles.

The system has received generally rave reviews from Tesla owners, though it was subject to some initial teething issues. The automaker hasn't said just what the take-rate has been for the option since it hit the market.

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