Tesla's Autopilot driver assistance system has had its share of controversy, but the latest Autopilot controversy stems from a third-party accessory.

An add-on weight dubbed Autopilot Buddy can allow drivers to keep their hands off a Tesla Model S or Model X steering wheel for extended periods of time, and can help to disable warnings that prompt the driver to take back control of the car.

A report on CNET last month highlighted the questionable device.

Autopilot Buddy is a small weight that attaches to one side of the steering wheel. It's designed to fool the car's Autopilot-linked torque sensor into thinking the driver has their hands on the steering wheel.

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Tesla’s Autopilot and several similar systems use torque sensors to ensure the driver has a hand (or hands) on the steering wheel. The Autopilot Buddy, which sells for $179, circumvents those sensors. In effect, it lulls the adaptive driver aids into an electronic stupor.

According to Autopilot Buddy's website, it works on Model S and Model X and the company is developing one for the Model 3.

According to a report in The Wall Street Journal, Tesla had considered installing additional sensors that would track the driver’s eyes to ensure they were looking forward and a different steering sensor that would detect the driver’s hands on the wheel. The paper reported the company chose not to use the additional sensors.

In a tweet, Tesla's CEO Elon Musk said his company had rejected the eye-tracking sensors "for being ineffective."

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Electronic driver aids such as automatic emergency braking, and active lane control constitute what are known as adaptive driver assistance systems (known as ADAS in Europe). They are designed to step in when a driver looks away momentarily.

They are not designed to take over driving for long periods of time. Most cars lack the lidar sensors and 360-degree cameras that can be used to detect lanes, obstacles, and traffic-sensors that are ubiquitous in autonomous test vehicles.

Tesla's Model S and Model X, like other cars with electronic driver safety aids, warn drivers frequently to keep their eyes on the road and their hands on the wheel. The legal status of devices that defeat those systems is unclear.