iDriveBAC is not a joke/gag app, nor is it a drink tracker. It is the only app on iTunes that can actually tell you if you're too intoxicated to drive. iDriveBAC works by measuring cognitive reaction time to a test devised from psychiatric journals and then calculating approximate BAC using a proprietary algorithm. A score of 85-92 correlates with a BAC of 0.08.

Neuropsychopharmacology (2006) 31, 1301–1309. doi:10.1038/sj.npp.1300941; published online 26 October 2005

J Stud Alcohol. 1990 Mar;51(2):114-22.