Quite simply, it's a breathalyzer mounted in the car of anyone charged with DWI, that decides whether or not they can drive. The system will disable the vehicle's starting components, making the car immobile until an acceptable blood-alcohol content reading is achieved. Video cameras may also supplement the breathalyzer in some cases, to document who actually blows, and who actually drives.
A sober driver is allowed to start his or her car and drive it just like anyone else, but is forced to re-do the breath test periodically during the trip to assure no alcohol has been consumed since the initial test. If any of these screenings are failed, the car will turn into an absolutely miserable environment. The horn will blow itself and the stereo will produce an unbearable high frequency, high intensity tone. The only way to stop the noise will be to shut the car down.
It's a pretty strict law, and will effect all members of the drunk driver's family. That is, anyone wanting to drive the person's vehicle will be required to complete the same tests. Now you're probably already thinking of a few people whose pickup trucks you won't be asking to borrow when you move. If you're concerned about tax payers footing the bill for this new law, don't worry too much. The installation and operation of the equipment is covered by the driver - and could add up to over $200 per month for some drivers.
Although I could rant for a while about drunk drivers, I'll conclude by saying that I'm all for the new requirement. These people should consider themselves fortunate to have a license at all. The law won't catch everyone, but it's a step in the right direction. People are sure to complain that it's an invasion of privacy, but I can't say I care a bit. I hope more states adopt the law. Maybe their speeds should be limited too. Hmm, 25mph sounds pretty safe right?