Support systems for automobile drivers have been recently developed. One support system prevents drivers from sleeping at the wheel, but an adequate system has not yet been commercialized. To detect the drowsiness level, methods can be divided into two categories. One category uses vehicle information, such as monitoring the car’s distance to the lane marker to detect how a driver is maneuvering the steering wheel. The other category uses physical information, such as brain waves, the electrical potential of the skin or heart, eye motion, and blinking information. Among these methods, blinking information is said to reflect drowsiness most easily. Many reports say that when a driver is drowsy, the blinking duration tends to be long. So, we propose a method to prevent drivers from sleeping by detecting the blinking duration. Because this method only uses simple image processing, the algorithm is not complex. We used a digital camera and PC because we wanted to use hardware that everybody can easily prepare. The algorithm involves face localization, then eye localization, followed by measurement of the blinking duration. We tested our system on a number of frames, and the correct blinking duration was usually detected.