Six states have no statewide law requiring an ignition interlock device for a DUI conviction: California, Indiana, Montana, Nevada, North Dakota, and South Dakota.1National Conference of State Legislatures. State Ignition Interlock Laws Another thirteen states require the device only when aggravating factors like a high blood alcohol concentration or a prior conviction are present. The remaining thirty-one states and the District of Columbia mandate an interlock for every DUI, including a first offense with no aggravating circumstances. So the states that do not require an ignition interlock as a matter of statute are a small minority, and even there a judge keeps the discretion to order one.
The Six States With No Statewide Mandate
In California, Indiana, Montana, Nevada, North Dakota, and South Dakota, no statute automatically forces any DUI offender to install an interlock.1National Conference of State Legislatures. State Ignition Interlock Laws A judge in any of these states can still order the device if the facts warrant it, but there is no automatic trigger written into the law. A first-time offender in Indiana who blows a 0.09 could leave court with a license suspension and probation and no interlock requirement at all, depending on the judge.
No mandate does not mean light consequences. Montana still imposes license suspension and may require alcohol treatment as a condition of probation. A judge who declines to order an interlock may instead impose stricter supervision, a longer suspension, or more frequent check-ins.
The Insurance Institute for Highway Safety tracks interlock requirements for first-time offenders across three situations: driving during an administrative license suspension, driving during a post-conviction suspension, and as a condition of reinstatement. Indiana, Montana, and Nevada show “no” in all three, confirming no mandatory interlock pathway for first offenders.2Insurance Institute for Highway Safety. Alcohol Interlock Laws California, North Dakota, and South Dakota have incentivized pathways where choosing an interlock may shorten a suspension, but the device itself remains optional.
The Thirteen States That Require an IID Only Sometimes
Thirteen states sit between full discretion and a blanket mandate. They require an interlock in defined circumstances and leave the rest to the judge. They break into two groups.
High BAC or Repeat Offense Triggers the Device
Eight states require an interlock when the offender’s blood alcohol concentration exceeds a set threshold or when the conviction is a repeat offense: Florida, Michigan, Minnesota, North Carolina, Pennsylvania, Rhode Island, Wisconsin, and Wyoming.1National Conference of State Legislatures. State Ignition Interlock Laws The BAC trigger varies. Michigan sets its threshold at 0.17 and Wisconsin uses 0.15. A first-time offender in any of these states who blows just above the 0.08 legal limit typically falls outside the mandate, though a judge can still order a device.
Wisconsin illustrates how these laws work. The state requires an interlock for all repeat OWI offenders, all first-time offenders with a BAC of 0.15 or higher, and anyone who refuses a chemical test at a traffic stop. A first offender who blows 0.10 and cooperates with testing falls outside every mandatory trigger.
Repeat Offenders Only
Five states reserve the interlock requirement for people with more than one DUI conviction: Georgia, Maine, Massachusetts, Missouri, and Ohio.1National Conference of State Legislatures. State Ignition Interlock Laws A first-time offender at any BAC level faces no automatic interlock in these states. The device kicks in only when a prior conviction makes the new offense a second or subsequent violation.
What Still Gets You an Interlock Where It Isn’t Mandatory
Even in the nineteen states without a universal mandate, certain facts almost guarantee a judge will order the device. If you are facing a DUI in one of these states, the written law is only part of the picture.
- A blood alcohol concentration well above 0.08 is the most common judicial trigger. States that set specific statutory thresholds use cutoffs between 0.15 and 0.17, and judges in the fully discretionary states tend to follow similar reasoning.
- A second or subsequent DUI within the state’s lookback period, which runs five to ten years in most jurisdictions, almost always draws an interlock order. Some states that leave first offenses to discretion make second offenses mandatory by statute.
- Refusing a breath or blood test carries its own administrative penalties, and many states treat a refusal as equivalent to a high-BAC result for interlock purposes.
- A DUI that involves a crash causing property damage or injury often draws an interlock order on severity grounds, even where one is not technically required.
Commercial Drivers Don’t Get a Pass
If you hold a commercial driver’s license, the state’s interlock law is not the controlling rule. Federal regulations require a minimum one-year CDL disqualification for a first DUI committed in any vehicle, and a lifetime disqualification for a second offense. An interlock cannot be installed on a commercial vehicle during that period because the CDL itself is suspended. Living in one of the six no-mandate states will not change the federal disqualification.
What Happens If a Judge Does Order One
Because every state leaves the interlock on the table through judicial discretion, it helps to know what the device actually does. An ignition interlock is a breathalyzer wired into the vehicle’s starting system. Before the engine will turn over, the driver blows into the device. If the breath sample registers above a preset threshold, usually around 0.02 or 0.025, the vehicle will not start.3National Highway Traffic Safety Administration. Ignition Interlocks – What You Need to Know The device also demands periodic breath samples while driving, called rolling retests. A failed rolling retest will not shut the engine off, but the horn and lights may activate, and the expected response is to pull over and stop as soon as it’s safe.
In most states the interlock is the mechanism that allows any driving at all during what would otherwise be a hard suspension. After a DUI-related suspension, a restricted license usually permits driving only in a vehicle equipped with a functioning device. Without the device, there is no legal driving until the full suspension expires. A first conviction with no aggravating factors typically draws six months to one year on the device, a second conviction adds one to two years, and a third or subsequent offense can mean three to five years or longer.
Research funded by the National Highway Traffic Safety Administration found that drivers with interlocks installed are 35 to 75 percent less likely to commit a repeat drunk-driving offense than convicted drivers without one.4National Highway Traffic Safety Administration. Case Studies of Ignition Interlock Programs That evidence is what has pushed thirty-one states and D.C. toward all-offender laws, and it’s also why judges in no-mandate states frequently order the device anyway when the facts give them a reason.