BreathalEyes is an iPhone app that detects jerking in the eye using the iPhone camera and analyzes the eyes jerking using the Horizontal Gaze Nystagmus field sobriety tests and estimates your blood alcohol ranging between .02 -.17.
One wonders with technology like this that costs .99 cents why law enforcement does not use it and at least record the jerking of the eyes for later use in court.
One caveat on the HGN is that the National Highway Transportation Safety Administration when validating HGN in laboratory tests found that HGN only correlates with a blood alcohol content over .10 with 6/6 clues 77% of the time.