It's very interesting when new people go on the interlock. They always test it to see if it actually works. So they actually take a couple of drinks, blow into it, and then find out it does work.
The second thing is there are a lot of phone calls in the first month, early in the morning, saying that the interlock doesn't work. What happens is they've been out drinking all night long, they've had five hours of sleep, and they have an elevated BAC. When they go to start the vehicle, they think that because they've done this all their life, their blood alcohol has gone away in those few short hours. In fact, it prevents them from driving in the morning. So it teaches them how to separate their drinking from their driving. That's one of the behavioural changes.
The cost is significant at $150, but if you work it out, it's about a drink a day. They have to reduce their drinking to be able to use the interlock kit effectively. So it actually pays for itself at the end of the time.