Eye tracking technology received new attention recently due to its inclusion in the Samsung Galaxy IV phone, where it can (with mixed results, according to reviewers) let users scroll the screen with their eyes or dim the screen when they look away. Clearly this is a technology that has the potential for a lot of clever applications. But what are the privacy implications?
Eye tracking for research was used for over a century before computers (see the quick history outlined in this article). The earliest research, in the 19th century, actually involved direct mechanical contact with the cornea. Already by 1898, researchers were discovering some really cool phenomena of the human brain. Motion pictures were applied to the problem as early as 1905, and the first head-mounted eye-tracker was developed in 1948, which freed study subjects from having to keep their heads still. In the mid-1970s the first remote trackers were developed that were truly unobtrusive to the subject. By then, research and writing based on eye tracking was booming, not only on the part of psychologists but also the military.