Breath Analyser in a car are annoying as hell. My friend had one installed when he got busted for DUI and he proved to the judge that he needed his car for his job.
1. You don't only blow in it to start the car. The machine will randomly ask you to breath again WHILE you are driving. Failure to do so in 10 minutes will shut down your engine. It's to make sure your friend didn't blow in it for you because you were drunk.
2. Result need to be examined once a month by an authorized person to make sure you didn't fail once and to make sure the machine is still correctly calibrated (Around here , they do that at a car windshield/window/radio shop chain).
3. These machine are rentals and they cost around 80$ per month ( including the cost of #2 ).
This will never be de facto installed in every car.