At this point, only a small proportion of convicted drunken drivers actually end up using the devices, says the U.S. Department of Health's Task Force on Community Preventive Services.

Even though most states use interlocks, they require them only under certain circumstances -- for example, with a particularly high blood-alcohol count or on a second conviction. (You can see your state's penalties -- and calculate your own safe-driving limit -- with CarInsurance.com's "What's Your Limit?" tool.)

Today, 14 states -- Alaska, Arizona, Arkansas, Connecticut, Hawaii, Illinois, Kansas, Louisiana, Nebraska, New Mexico, New York, Oregon, Utah and Washington -- require ignition interlock devices for every convicted drunken driver.

Car insurance won't pay the bill

As you'd imagine, wily drivers try to fool ignition interlock devices, getting others -- even children -- to blow into the devices for them. They also try using canned air and other evasions.

But device makers keep improving the technology. Devices now include "running retests" -- drivers are periodically required to pull to the side of the road and submit to another test within a brief time span. If a driver flunks the retest, the car keeps running -- it might be dangerous to immobilize it -- but the horn honks and the lights flash to summon police. (Here's a MADD FAQ on the devices.)

You not only blow into the device but also pay for the privilege. Private companies usually provide the services. Installation can cost as much as $200, and monthly fees range from $50 to $100.

The cost of an ignition interlock device isn't covered under your car insurance policy, which, of course, you'll be paying more for as well. Analysis of rates pulled through CarInsurance.com's car insurance comparison tool suggests you should expect your insurance rates to double. Surcharges for a drunken-driving conviction do vary widely from state to state and even more so from insurer to insurer.

Although makers of ignition interlocks have proposed otherwise, no insurance company offers a discount for installation of a device.

How about some old-fashioned jail time?

Despite the apparent effectiveness of interlocks, many other tactics still are in use. They include:

License suspension and jail time. In all states but Wisconsin (where it's a traffic ticket), driving while intoxicated is a crime. Officers make 1.4 million DUI arrests each year, says MADD. Every state defines drunken driving as having a blood alcohol content of 0.08% or more. In all states and Washington, D.C., it's illegal to buy alcohol before age 21, and the legal blood alcohol limit is lower for teens -- 0.02% for drivers under 21 vs. 0.08% for those over 21.

But beyond that, penalties -- and their application -- diverge a lot. Some states let you refuse a Breathalyzer test please submit to having your license revoked. Some mandate jail time, even for first-time offenders, but in practice offer diversion programs with alternative penalties like community service, monitoring, treatment or license revocation.

Vehicle seizures. Some states allow communities to seize -- and sometimes even sell -- vehicles belonging to people convicted of driving drunk. Stiff impound fees and penalties must be paid to redeem the vehicle. But the approach isn't catching on, Harris said, probably because exceptions -- other family members need to drive, for example -- make the programs difficult to enforce.

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Special license plates. A few states assign special vehicle plates, or a series of license-plate numbers, to convicted drunken drivers. Ohio uses red and yellow plates different from other state licenses on vehicles that have been impounded for drunken driving. Georgia and Minnesota use special plates on a limited basis. Oregon and Iowa have experimented with similar programs that aren't currently active. Special plates aren't a widely used tactic. Here's a roundup of state special license laws, from the National Conference of State Legislatures.

The bottom line, interlock advocates say, is that even when jail time is served, it doesn't teach the convicted person how to drive sober. It is hoped that ignition interlock devices will do so.