An image-processing computer system developed by Toyota Motor Corporation and a Toyota affiliate uses a camera near the steering wheel to detect when the driver stops looking straight ahead.
The system flashes a light on the dashboard display and emits a beeping noise when the eyes start to wander.
If the driver still doesn't respond, brakes kick in, Toyota said on Tuesday. The feature will be offered in Lexus luxury models set to be sold in Japan in spring next year.
Toyota did not comment on whether it will be offered in models sold abroad, company spokeswoman Keiko Nakajima said.
Research shows that most accidents happen because the driver isn't paying attention, according to Toyota.