Spitballing here, but let's imagine a common impaired driving situation- being very sleepy and needing to get somewhere on a time-schedule.
I don't know if you've ever been in that situation, but it's possible to fall all the way asleep while driving. It's such a common thing that they carve rumble strips into the sides of highways.
Being so sleepy is a tricky thing. You can fall asleep even with the radio going full blast. I can't imagine any alarm system that would stop someone being lulled to sleep by the engine and movement of a car doing 90% of the driving.
I don't know if you've ever been in that situation, but it's possible to fall all the way asleep while driving. It's such a common thing that they carve rumble strips into the sides of highways.
Being so sleepy is a tricky thing. You can fall asleep even with the radio going full blast. I can't imagine any alarm system that would stop someone being lulled to sleep by the engine and movement of a car doing 90% of the driving.