Several thousand Illinois residents won't be able to hop in their cars and leave if they have one too many drinks at a Fourth of July party, thanks to a new law that already may be saving lives here and in other states.

The law, which took effect Jan. 1 in Illinois, requires first-time drunken driving offenders to install breath-monitoring gadgets that prevent engines from starting until motorists blow into the alcohol detectors to prove they are sober.

At least 7,000 Illinois residents have had to use the devices so far this year - up from around 3,000 in all of 2008 under an old law that mostly targeted multiple DUI offenders. At least 5,000 more people could install them by the end of 2009, according to data obtained by The Associated Press from the Illinois secretary of state's office.

Despite a few reported problems, both officials responsible for overseeing its implementation and at least some attorneys are giving the law high marks.

The dashboard devices, called interlocks, are mandated only for the six to 12 months licenses are typically suspended with a first DUI. Drivers may opt not to install them, but then would be banned from driving during the suspension period. Users must pay for the fist-size devices, which cost hundreds of dollars.

New Mexico in 2005 became the first state to mandate interlocks. A handful of states, including Arizona, Louisiana, Washington, Nebraska, Alaska and Colorado, have similar laws.

MADD wants every state to pass such a law, arguing that could substantially reduce the number of DUI deaths nationally each year, now at around 15,000. A 2008 study by the Pacific Institute for Research and Evaluation found interlocks helped decrease repeat offenses in New Mexico by approximately two-thirds.

Chicago-based DUI lawyer Harold Wallin said he was surprised only 7,000 Illinois residents have used the devices so far this year, given that about 40,000 are arrested annually for DUIs - mostly first-time offenders.

Several of Wallin's clients have complained their cars didn't start after they rinsed with mouthwash, then blew into the interlocks. In one instance, he said, the device seemed to mistake vapor from window-cleaning fluid for alcohol, preventing a client from starting the engine.

New Mexico has seen its drunken-driving deaths fall 20 percent since its law took effect, according to MADD. The group believes other states could see the same percentage decline within a few years.

Motorists could try to skirt the devices by, say, having someone else blow into detector or driving someone else's car. But if caught trying to circumvent the interlocks in Illinois, they could go to jail for up to three years.