Many years ago I was involved with an engineering design project involving drunk driving. We got a breathalyzer and recruited a guy that drank a lot. Back then 0.15 was the legal limit, He couldn't stand up at that level. What we found was that being able to punch numbers to gain entry was not a good event for testing for impairment. The only one that made sense was blood alcohol level because that was the law so we designed an ignition interlock system based on what the driver blew.
