Once the car is on the road, a camera mounted on the steering wheel monitors the driver's face, looking for signs that he or she is dozing off.

This system, developed by Nissan in conjunction with unidentified partners, uses facial-recognition technology that identifies a broad range of features--eyes, nose, mouth, and so on--before focusing on the eyes. A calibration tool learns an individual's patterns of opening and closing his or her eyes, turning this into what Nissan calls a closed-eye ratio. Because of the wide variation from individual to individual, blinking is excluded from this ratio, Steeden says.

If a driver's eyelids begin to droop, closing for longer than the normal ratio would predict, the system triggers the audio and navigation-screen warning, and it tightens the driver's seat belt in an attempt to gain his or her attention.

This system, too, has its weaknesses. The recognition system today works only if the eyes are clearly visible, which means that sunglasses, glasses with reflecting surfaces, or even thick frames that obscure the eyes could disable the tool, Steeden says.

Finally, a third set of tools monitors driving activity. External cameras paired with image-recognition software that identifies lane markings on the road are already employed in some Nissan models as a lane-departure warning system. The concept car uses this, along with steering-wheel position sensors, to detect erratic driving behavior.

As with the facial-recognition technology, abnormal behavior such as veering in and out of lanes will trigger the audio and navigation display screen warnings, and the seat belt will again tighten slightly to attract the driver's attention.

As yet, the company has no immediate plans to make these tools, demonstrated last week inside an otherwise ordinary Fuga sedan (known as the Infiniti M45 in the United States), available to consumers.

"This system is a concept, and there is no confirmation of if or when it may be used on future production vehicles," Steeden says. "It is, however, a subject of discussion currently being undertaken by government officials and JAMA [the Japanese Automobile Manufacturers' Association] in Japan."

Nissan's concept car goes well beyond what most other car makers have announced, but the industry as a whole is looking hard at this kind of automatic system.

Volvo has developed a "multilock" system that requires a driver to blow into a Breathalyzer in the seat belt and then buckle up before the car will start. Saab is testing an "AlcoKey" tool--essentially a mini-Breathalyzer about the size of a small mobile phone--that would transmit an electronic signal to the car, allowing it to be started.

Some U.S. states have already begun to require people convicted of driving under the influence to install Breathalyzers, called ignition interlock devices, that can prevent a car from starting following a test that reveals high blood alcohol content.