[themaninthedark]

That is less invasive than making you blow. But there will always be edge cases.

Imagine a medical condition that makes it look like you are impaired. Now, you have to go to the dealer with a doctor's note to get this system disabled. Or when you want to rent a car.

Or, if there is a case when driving impaired would be better then the alternative. You and a friend are camping in the woods out of cell range, you both have some beers then one of you trips and gets a deep cut on the leg. Now you have to wait a couple hours before he can drive you to where you can get cell signal, hope you don't bleed out.