Why Do States Require Ignition Interlock Devices?

Over the last 15 years, many states have started using ignition interlock devices (IIDs) to help prevent drunk driving. These devices act like a breathalyzer and are connected directly to a car’s ignition system.

Before a vehicle can start, the driver must blow into a mouthpiece to check their blood alcohol concentration. If the BAC is below the legal limit, the car starts. If it's above, the device stops the car from starting until the driver provides a clean reading. This helps ensure that only sober drivers can operate the vehicle.

Some IIDs also require rolling retests after the car has started. This means the driver has to blow again to confirm that they were the one who provided the initial sample. The device doesn’t shut the car off immediately, but it records the event and warns the driver to stop safely. This data is then sent to the DMV for monitoring.

All States Now Require IID Laws

By 2020, every state had some form of law requiring ignition interlock devices for DUI offenders. New Mexico was the first to implement this in 2005, mandating IIDs for all convicted drunk drivers. Between 2006 and 2017, the state saw a significant drop in drunk driving incidents—over 70,000 cases prevented by IIDs alone.

This success led other states to follow suit. Some only require IIDs for repeat offenders, while others, like Connecticut, apply the rule to all DUI offenders, even first-time ones. Studies show that all-offender states experience a bigger reduction in drunk driving accidents and fatalities. Today, 34 states and the District of Columbia have such laws in place.

In Connecticut, IIDs aren't just for DUIs. They're also required if you:

• Failed or refused a chemical test for alcohol.
• Were caught driving under the influence of drugs.
• Caused vehicular assault or manslaughter.

Data Shows IIDs Work

The CDC found that IIDs reduce DUI offenses by up to 70%. However, the biggest challenge is ensuring that people actually install and maintain the devices. MADD also supports the effectiveness of IIDs, reporting that they cut repeat DUIs by 67% and reduce drunk driving deaths by 15%. They consider IIDs the most reliable way to keep impaired drivers off the road.

IIDs Are Needed for a Hardship License

Some states offer hardship licenses to individuals with a DUI, allowing them limited driving privileges, such as commuting to work or school. To qualify, these drivers must install an IID before being granted any driving rights. This ensures that even with restricted access, they remain sober behind the wheel.