Now, there is an App called BreathalEyes, available for the iPhone 4, that could very well serve to save your life – or that of a loved one. The App employs a method commonly used by law enforcement as part of a field sobriety test to determine whether a driver should be cuffed or not. The method tests for Horizontal Gaze Nystagmus (HGN), which is the involuntary jerking or bouncing of the eyeball that happens when enough alcohol has been imbibed to hinder the brain’s ability to control eye movement.

BreathalEyes utilizes the iPhone’s camera to identify any irregular movement in its subject’s eye. Users would enable the app, have their friend who has been drinking face the camera, capture their eye in a green rectangle on the iPhone’s screen, and then ask him or her, “…without moving your head, look as far to the side as possible for 10 seconds.” The user then taps the green rectangle three times, signaling the iPhone to begin its scan for HGN, upon which data is collected and analyzed to gauge the subject’s blood alcohol level.

To ensure the application’s precision, the creators of the program ran it through a series of tests in conjunction with an actual breathalyzer. BreathalEyes possesses an accuracy level of 0.02% – 1.7% (+/- .02%) BAC.

It is of course important to note that the App is not 100% accurate – therefore drivers and administrators of the App should know that the very best decision when drinking is to not get behind the wheel no matter how much alcohol has been consumed. Even if you used iphone jailbreak software to hack into your phone the app should still work fine.