Drunk Driving

I'm a hardliner on this issue, and stories like this just make me more convinced that I am right: http://www.cbc.ca/canada/montreal/story/2007/05/11/qc-methotdeath0511.html. I have to wonder how hard it would be to build cars which contain some type of breathalyzer/interlock device. Blow into a tube and the the car wont' start if you blow a 0.8 or higher. Every car should have this. How hard could it possibly be?