EXCEPT THEY NEED TO BE UNIVERSAL AND MANDATORY, LIKE SEAT BELTS:

The Breathalyzer Behind the Wheel (PHILIP J. COOK and MAEVE E. GEARING, 8/31/09, NY Times)

People driving while intoxicated still cause about 13,000 deaths a year in the United States. And of the 1.4 million arrests made, one-third involve repeat offenders. The greatest potential of ignition interlocks is to reduce this recidivism. [...]

A person who has been drinking might naturally think of fooling the device by persuading a sober person to start the engine, but that is not enough to subvert the system, because the device requires breath samples while the person drives — at random intervals of five minutes to an hour. (At least one company is also integrating cameras with the interlocks to photograph the driver when he provides a breath sample.) The unit keeps a log of all tests, and it is sealed so that any attempts at tampering can be detected.

Ignition-interlock devices are not perfectly effective; a drunk can often borrow another car. But in one recent study they were found to reduce repeat drunk-driving offenses by 65 percent. If they were widely installed, the devices would save up to 750 lives a year, a recent National Highway Transportation Safety Administration report estimated.