Had one for 2 years. In my state, the interlock violates at 0.02 bac, so everything set it off. I had to have some contested because it is triggered by windshield fluid methanol, and other alcohols.
I had violations due to drinking the night before, so I had to limit my drinking to 3 beers before 8pm if I wanted to start my car by 8am. If you're still drinking, I recommend getting an in home breathalyzer so that you don't trigger the interlock. My rules were set so I couldn't have 3 violations in a year. I had 5 that were not related to me drinking alcohol. Also beware, it picks up on every kind of alcohol, whether it be ethanol, methanol, or Isopropyl...