What is an Ignition Interlock Device (IID)? 2025 Guide

Intro

An Ignition Interlock Device (IID), often referred to as a "car breathalyzer" or "blow and go," is a sophisticated electronic device installed in a vehicle that prevents the engine from starting if it detects alcohol on the driver's breath. It's a key tool in the ongoing global effort to prevent impaired driving and enhance road safety, frequently mandated by courts or motor vehicle departments as a consequence of a Driving Under the Influence (DUI) or Driving While Intoxicated (DWI) conviction.

How Does an Ignition Interlock Device Work?

The operation of an IID is relatively straightforward for the user, though the technology behind it is quite advanced. Here's a breakdown:

  1. Initial Breath Test: Before starting the vehicle, the driver must blow into a mouthpiece attached to the IID.
  2. Alcohol Detection: The device uses a highly sensitive fuel cell sensor to detect the presence of alcohol (ethanol) in the breath sample. If alcohol is present, it generates an electrical current, the strength of which corresponds to the Blood Alcohol Concentration (BAC).
  3. BAC Threshold: The IID is programmed with a pre-set, very low BAC threshold (often as low as 0.02% or 0.025%). If the driver's breath sample exceeds this limit, the device will prevent the vehicle's ignition from engaging.
  4. Rolling Retests: To ensure continued sobriety while driving, the IID requires periodic "rolling retests." At random intervals after the vehicle has started (typically every 5 to 15 minutes), the device will prompt the driver to provide another breath sample.
    • Safety Feature: Importantly, the IID will not shut off the engine if a rolling retest is failed or missed. Doing so would create an unsafe driving situation. Instead, it will log a violation, and the vehicle's lights may flash or the horn may honk to alert others.
  5. Data Logging and Reporting: The IID records all activity, including passed and failed tests, ignored rolling retests, and any attempts to tamper with or bypass the device. This data is regularly downloaded (usually during scheduled calibration appointments) and reported to the monitoring authorities (court, DMV, or probation officer).
  6. Lockouts: If a driver fails multiple tests or attempts to bypass the device, the IID may enter a "lockout" mode, preventing the vehicle from starting until it is serviced by an approved installer.

Why are IIDs Used?

The primary purpose of an IID is to prevent repeat impaired driving offenses. By physically preventing a vehicle from starting if alcohol is detected, IIDs act as a deterrent and a monitoring tool. They are commonly ordered in DUI/DWI cases to:

  • Protect Public Safety: Directly reduce the risk of individuals driving under the influence.
  • Allow Restricted Driving Privileges: In many states, IIDs allow offenders to regain limited driving privileges (e.g., for work, school, or medical appointments) rather than a full license suspension, provided they drive sober.
  • Promote Accountability: Hold convicted impaired drivers accountable for their actions and encourage behavioral change.
  • Reduce Recidivism: Studies have shown that IIDs are highly effective in reducing drunk driving recidivism while they are installed.

Who is Required to Have an IID?

Laws regarding IID requirements vary significantly by state and even by jurisdiction. However, common situations where an IID may be mandated include:

  • Repeat DUI/DWI Offenders: Most states require IIDs for individuals with multiple impaired driving convictions.
  • First-Time DUI/DWI Offenders: An increasing number of states are implementing "all-offender" IID laws, requiring even first-time offenders to install the device.
  • High BAC: If the driver's Blood Alcohol Concentration was significantly above the legal limit (e.g., 0.15% or higher).
  • DUI with Injury or Minor in Vehicle: Cases involving an accident with injuries or having a minor passenger often trigger mandatory IID installation.
  • As a Condition of Probation or License Reinstatement: Courts or DMVs may require an IID as a condition for probation or for regaining driving privileges.


Costs and Maintenance

The cost of an IID typically includes an installation fee, a monthly leasing fee, and calibration fees. These costs are usually borne by the offender. While varying by provider and state, expect to pay:

  • Installation: $70 - $150 (one-time fee)
  • Monthly Lease: $60 - $90
  • Calibration: $20 - $50 (every 1-3 months)

Some states offer financial assistance programs for low-income individuals to help cover these costs. Regular calibration and maintenance by an approved service center are essential to ensure the device's accuracy and compliance.

Limitations and Common Misconceptions

  • Not Foolproof: While effective, IIDs are not immune to attempts at circumvention (though penalties for tampering are severe) or occasional "false positives" from substances like mouthwash or certain medical conditions (e.g., diabetes leading to acetone on breath). Users are often advised to rinse their mouth with water before testing.
  • No Automatic Engine Shut-Off: As mentioned, IIDs will not shut off a moving vehicle for safety reasons.
  • Discreet Placement: While the mouthpiece is visible, the main unit is often discreetly installed.

The Ignition Interlock Device serves as a powerful deterrent and a crucial tool in the fight against impaired driving, promoting responsible choices and safer roads for everyone.


Learn More About DUI Laws in Your State:

For specific IID laws, requirements, and resources in your area, please visit our Laws by State page.

Legal Disclaimer 

This site is for informational purposes only and is not legal advice. For help with your specific case, consult a licensed DUI attorney.

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