A Draeger ignition interlock device (red arrow) in a Scania bus

An ignition interlock device or breath alcohol ignition interlock device (IID or BAIID) is a breathalyzer for an individual's vehicle. It requires the driver to blow into a mouthpiece on the device before starting or continuing to operate the vehicle. If the resultant breath-alcohol concentration analyzed result is greater than the programmed blood alcohol concentration (which varies between countries), the device prevents the engine from being started. The interlock device is located inside the vehicle, near the driver’s seat, and is directly connected to the engine’s ignition system.[1] It is a form of electronic monitoring.

An ignition interlock interrupts the signal from the ignition to the starter until a valid breath sample is provided that meets maximal alcohol guidelines in that jurisdiction. At that point, the vehicle can be started as normal. A breath sample is not required to start the vehicle if the engine has been running within a time-out period, to allow quick re-starts in case the vehicle stalls. At random times after the engine has been started, the IID will require another breath sample, referred to as a rolling retest. The purpose of the rolling retest is to prevent someone other than the driver from providing a breath sample. If the breath sample isn't provided, or the sample exceeds the ignition interlock's preset blood alcohol level, the device will log the event, warn the driver, and then start up an alarm in accordance to state regulations (e.g., lights flashing, horn honking) until the ignition is turned off, or a clean breath sample has been provided. A common misconception is that interlock devices will simply turn off the engine if alcohol is detected; this would, however, create an unsafe driving situation and expose interlock manufacturers to considerable liability, which is why ignition interlock devices do not have an automatic engine shut off feature.


The first performance based interlocks were developed by Borg-Warner Corp. (now BorgWarner, Inc.), in 1969. In 1981, Jeffrey Feit, a student in New Jersey, placed in a statewide innovation contest with a primitive schematic of a breathalyzer based interlock device. In 1983, Hans Doran, a student in Limerick, presented a working prototype at the Young Scientist competition in Dublin. Alcohol-sensing devices became the standard through the 1980s. They employed semiconductor (nonspecific) alcohol sensors. Semiconductor-type (Taguchi) interlocks were sturdy and got the field moving, but did not hold calibration very well, were sensitive to altitude variation, and reacted positively to non-alcohol sources. Commercialization and more widespread adoption of the device was delayed pending improvement of systems for preventing circumvention. By the early 1990s, the industry began to produce “second generation” interlocks with reliable and accurate fuel cell sensors. All current ignition interlocks are required to meet National Highway Traffic Safety Administration (NHTSA) standards.


Modern ignition interlock devices use an alcohol-specific fuel cell for a sensor. A fuel cell sensor is an electrochemical device in which alcohol undergoes a chemical oxidation reaction at a catalytic electrode surface (platinum) to generate an electric current. This current is then measured and converted to an alcohol equivalent reading. Although fuel cell technology is not as accurate or reliable as infrared spectroscopy technology used in evidentiary breathalyzers, they are cheaper and tend to be more specific for alcohol. Alcohol, as defined here, includes isopropanol, sorbitol, menthol, methanol, and a host of other types of alcohols, in addition to ethanol (consumed liquor).

The devices keep a record of the activity on the device and the interlocked vehicle's electrical system. This record, or log, is printed out or downloaded each time the device's sensors are calibrated, commonly at 30-, 60-, or 90-day intervals. Authorities may require periodic review of the log. If violations are detected, then additional sanctions can be implemented.

Periodic calibration is performed using either a pressurized alcohol–gas mixture at a known alcohol concentration, or with an alcohol wet bath arrangement that contains a known alcohol solution. The costs of installation, maintenance, and calibration are generally paid by the offender. On average, ignition interlock devices are about $70–150 to install and about $60–90 per month for monitoring and calibration.[2]

Many countries are requiring the ignition interlock as a condition for drivers convicted of driving under the influence, especially repeat offenders. Most US states now permit judges to order the installation of an IID as a condition of probation; for repeat offenders, and for first offenders in some states, installation may be mandated by law.

Some IIDs are equipped with cameras, which may be required by the jurisdiction or voluntarily used. The purpose of the camera is to identify "fail" results with the driver, which conveniently makes it easier to "clear" test failure reports when the "fail" result was triggered by a third party.



Interlock devices are used in the states of Victoria,[3] South Australia,[4] Western Australia,[5] Tasmania,[6] New South Wales,[7] and Queensland. The Northern Territory and the ACT are also looking into their use.


Interlock systems were introduced in 2017.


Laws permitting judges to impose the use of interlock devices on convicted drunk drivers permitted their use from 2010, however by 2016 it had only been used in 55 cases. The cost, €3,500 to be paid by the driver, is a deterrent to its use. From 2017 the device may be paid from the fines imposed on the driver and in addition it may become compulsory for repeat offenders.[8]


Some provinces, such as Ontario,[9] Quebec,[10] and Manitoba[11] require any person convicted of drunk driving or refusing to provide a breath sample, to install an ignition interlock device into any vehicle he or she owns or operates, for a specified period of time (or for life), depending on the number of prior drunk driving offenses.

After so many drunk driving convictions, some provinces, such as Nova Scotia,[12] will impose a lifetime driving ban, with no possibility of license reinstatement. Ontario[13] courts, however, have the power to enact lifetime driving bans, with no possibility of reinstatement, after so many Criminal Code driving convictions. Under such circumstances, ignition interlock conditions are not put in place on the person's license.


In Finland, interlocks were first trialled in 2005. It was put into legal effect in 2008. Installation costs around €2400 for one year, €1920 per year for two year, or €1440 per year for three years.[citation needed] Only 5.7% of the drivers re-offended instead of 30% without the program. The relevant administration is the Finnish Transport and Communications Agency Traficom.[14]

In Finland, there are approximately 1,000 drivers participating in the Ignition Interlock Device program.[15]


In France, 1,500 Ignition interlock devices were installed.[when?][16]


From December 2011 the Netherlands started to use an interlock device for offenders who were caught with a blood alcohol level over a certain limit. The process which had over 5,000 participants was cancelled in 2015 due to legal and technical problems.[17]

New Zealand

Alcohol interlock devices became a sentencing option in New Zealand in August 2012. In December 2012, it was reported that the first device had been installed.[18]


Alcohol interlock devices are used in buses at least in Stockholm.[19]

United States

As of 2012, all 50 states have laws permitting the imposition of ignition-interlock devices as sentencing alternatives for drunk drivers.[20] It is estimated that the United States could be saving 800 lives per year if all convicted drunk drivers were prevented from being involved in a fatal crash.[21] The standard device in the US consists of a mouthpiece mounted on a handheld unit and a cord that attaches to the vehicle’s ignition system and runs on the battery. The driver is required to blow into the mouthpiece to test his or her alcohol level before starting the car.[22] Devices are required to be installed at a certified service center. Devices are shipped directly to the qualifying service center and are never handled by the customer. The largest ignition interlock device providers are Draeger, Smart Start, Guardian, Intoxalock, and LifeSafer.

General implementation of IID requirements in the US

Most states impose the installation of ignition interlock devices (IID), with varying thresholds for installation requirements.[23][24] Criminal process thresholds for installation requirements vary between minimum BAC levels (e.g., 0.20%, or 0.15%) or repeat offense, with about half of the states requiring installation on first offense.

These ignition interlock sanctions are meant as punishment, but also as a deterrence. When required under a high BAC level or multiple offense threshold, ignition interlock requirements address a strong tendency of repeat offense by drivers with alcoholic use disorder (AUD or alcoholism).

Ignition interlock requirements are also imposed in some instances after positive chemical blood alcohol tests, as a physical deterrent for drivers with alcoholic use disorder, or as a pseudo-civil punishment. Ignition interlock requirements are also imposed in some instances after an implied consent refusal under similar forensic procedures.

Zero tolerance threshold

In most US implementations, IIDs are set to a "zero tolerance" level (set to either levels consistent with culinary alcohol or measurement errors).


In operation, the driver blows into IIDs to enable the car's starter. After a variable time period of approximately 20–40 minutes, the driver is required to re-certify (blow again) within a time period consistent with safely pulling off the roadway. If the driver fails to re-certify within the time period, the car will alarm in a manner similar to setting off the car's immobilizer, but mechanically independent of it. The installation company may provide regular reports to the Department of Motor Vehicles of a driver's home state regarding its usage.[25]

Restrictions on operation and repair by others

Various US states have different penalties for disabling IIDs. In some cases, the driver may be penalized if a family member or mechanic disables the IID when not in use by the sanctioned individual, or temporarily for servicing the vehicle. In some implementations, disabling by mechanics and others is either permitted or authorisation easily obtained, but some jurisdictions restrict or deny authorisation. (Such restrictions on mechanics can be problematic, for example, if limited to designated "licensed mechanics" or as applied to routine repair procedures requiring operation of the ignition and starter systems.) Some jurisdictions criminalize such temporary bypass of IIDs.


Violations can occur from a driver not having reached the "zero tolerance" level, but can also occur from use by other drivers within legal limits, or from test anomalies. In some states, anomalies are routinely discounted, for example as not consistent with patterns of BAC levels or at levels incompatible with life (e.g., significant mouth alcohol - if read as BAC would mean the patient is dead). In some states, "fail" readings inconsistent with actual alcohol use can be cleared by a routine process, but other states automatically deem these "fail" readings as violations.

Individual state provisions


"DUI Offenders may be required to obtain an Ignition Interlock Device (IID)."[26]


Arizona offers what is called a Special Ignition Interlock Restricted Driver's License In Lieu of mandatory license suspension. It is a type of restricted driver's license that is used to facilitate the Ignition Interlock Requirement in a Vehicle. The time that the SIIRDL is required varies greatly. For example, in the event of a first time Implied Consent Refusal, it can be up to one year. [27] All IIDs must be installed by an approved company, and must be equipped with a camera, GPS and real-time reporting capabilities.[28]


As of July 1, 2010, California implemented a pilot project for DUI sentencing, as a pilot program involving four counties under AB 91: Alameda, Los Angeles, Sacramento, and Tulare. Under the pilot project, if driving on a suspended license due to a DUI conviction, legally the court must impose an ignition interlock device requirement for up to a maximum of three years from the date of conviction. As of July 1, 2010, interlocks are required upon a DUI conviction in the four counties.

In the four counties under the AB 91 pilot program, all drivers convicted of a DUI offense are required to install IIDs in their vehicles as a condition to receive restricted driving privileges. First offenders convicted of drunk driving are required to install an ignition interlock device in their car for a period of five months and second offenders for a period of one year.[29] Previously, this requirement was only required for third offenders and permitted for second offenders, and then for a three-year period. The California DMV has written guidelines to clear up some ambiguities in the law. Costs associated with ignition interlock devices include $70 – $150 for installation and fees in the range of $60 - $80 per month thereafter.[30]

SB 598 shortens the amount of time certain repeat DUI offenders will have to wait before becoming eligible to apply for restricted California driving privileges. To receive the restricted license, though, these drivers will be required to meet certain criteria, such as the installation of an IID in their vehicles.[31]


First-time DUI convictions result in one year of a mandatory ignition interlock device.[42] A second conviction requires the IID be installed for at least five years, and on a third offense or greater, the requirement becomes at least ten years. Some convictions of negligent driving or reckless driving can require the convicted person to use an IID for a period of six months or longer.


Starting January 1, 2006, drivers that had a second or subsequent operating under the influence offense and are eligible for a hardship license or for license reinstatement, are required to have an ignition interlock device attached to their motor vehicle, at their own expense.[32]

New Jersey

Senate bill S824 decreases the length of driver’s license suspensions for drunk driving and refusing to submit to a breathalyzer test, but increases ignition interlock device requirements for these offenses. All first-time DWI offenders in the state of New Jersey are required to install an ignition interlock device on their vehicle.[33] Also, if your license has been revoked for failure to submit to an alcohol test, you can regain your driving privileges if you install an ignition interlock.[34]

New Mexico

Ignition interlocks are required for at least one year for all first-time DWI offenders; subsequent offenses require longer periods of installation.[35] Also, if your license has been revoked for failure to submit to an alcohol test, you can regain your driving privileges if you install an ignition interlock.[36]

New York

Don Prudente from DriveSafe Ignition Interlock of New York, Inc. states that as of August 15, 2010, New York state requires a person sentenced for Driving While Intoxicated have an ignition interlock device installed for at least 6 months on any vehicle they own or operate, and the driver have an "ignition interlock" restriction added to their driver license.[37] This was mandated in honor of Leandra Rosado who died riding in a vehicle driven by a drunk driver.

North Carolina

A conviction of Driving While Impaired with a blood alcohol concentration of 0.15 or more or another conviction within the past seven years will require an ignition interlock device to be installed on the vehicle.[38]

Rhode Island

As of 2015, Rhode Island courts have had the power to grant a hardship license to DUI offenders following the installation of an ignition interlock device. First-time DUI offenders can be required to use the IID for three months to one year. A second conviction can require IID usage for six months to two years. A third conviction can require IID usage for one to four years, while a third conviction within five years can require IID usage for two to 10 years.[39]


As of Sept 1, 2015, anyone arrested for driving over the legal limit of .08% can opt for an IID restriction rather than wait for their driver's license suspension period to be up. For BAC levels .15% and over, Texas courts require IIDs, even for first time offenders.[40]


Effective July 2, 2009, anyone convicted of a DUI, whether it be a first offense or a subsequent offense, will be required to have an ignition interlock device placed on their car — for 18 months for first time offense.[41]


Effective July 1, 2012, anyone who is convicted of DUI may drive only with an ignition interlock after the first offense, as a condition of a restricted license and is required to have an ignition interlock installed in each vehicle owned by or registered to him after a second offense for a period of six months. The bill also provides that the court may authorize a restricted license for travel to and from the interlock installer and a person can pre-qualify for an ignition interlock prior to conviction.[42]


First-time DUI convictions result in one year of a mandatory ignition interlock device.[43] A second conviction requires the IID be installed for at least five years, and on a third offense or greater, the requirement becomes at least ten years. Some convictions of negligent driving or reckless driving can require the convicted person to use an IID for a period of six months or longer.

Universal IID installation

Proposals have been made to install IIDs on all new vehicles, set to the legal limit for the driver. Some politicians in Sweden,[44] Japan, Canada, the US, and other countries have called for such devices to be installed as standard equipment in all motor vehicles sold.[citation needed]

Issues to be solved, besides consumer and voter acceptance, include difficulty in obtaining accurate measurements without inconvenience, and a need to achieve high reliability, in order not to interfere with vehicle usability.

See also


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  2. ^ "Ignition Interlock FAQ's". Archived from the original on 2016-04-02.
  3. ^ "About the Victorian Alcohol Interlock Program". vicroads. Archived from the original on 5 April 2018. Retrieved 23 May 2018.
  4. ^ "Towards Zero Together: The Mandatory Alcohol Interlock Scheme". South Australia Department of Planning, Transport and Infrastructure. Archived from the original on 21 March 2018. Retrieved 23 May 2018.
  5. ^ News, A. B. C. (4 October 2016). "Drink drivers to be forced to use alcohol interlocks from this year, WA Minister says". ABC News. Archived from the original on 6 April 2017. ((cite news)): |last1= has generic name (help)
  6. ^ "Mandatory Alcohol Interlock Program". Tasmanian Department of State Growth. Archived from the original on 13 March 2018. Retrieved 23 May 2018.
  7. ^ "Mandatory Alcohol Interlock Program". NSW Roads and Maritime Services. Archived from the original on 7 May 2018. Retrieved 23 May 2018.
  8. ^ "Ignition interlock device soon to become a popular punishment". expatica.com. 4 April 2017.
  9. ^ Government of Ontario, Ministry of Transportation. "Impaired Driving - Ignition Interlock Program". www.mto.gov.on.ca.
  10. ^ "Archived copy" (PDF). Archived from the original (PDF) on 2014-12-23. Retrieved 2013-11-18.((cite web)): CS1 maint: archived copy as title (link)
  11. ^ "Ignition Interlock Program". www.mpi.mb.ca. Retrieved 2023-01-25.
  12. ^ "Service Nova Scotia - Registry of Motor Vehicles - Alcohol and Driving". novascotia.ca.
  13. ^ Other ways to lose your licence | Ontario.ca
  14. ^ https://etsc.eu/wp-content/uploads/ALCOHOL_INTERLOCKS_FINAL.pdf[bare URL PDF]
  15. ^ https://etsc.eu/wp-content/uploads/ALCOHOL_INTERLOCKS_FINAL.pdf[bare URL PDF]
  16. ^ https://etsc.eu/wp-content/uploads/ALCOHOL_INTERLOCKS_FINAL.pdf[bare URL PDF]
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  18. ^ Maas, Amy (30 December 2012). "Six beer habit earns first interlock". The Press. Retrieved 30 December 2012.
  19. ^ "The Swedish Transport Agency and our work with an alcohol interlock program" (PDF). etsc.eu.
  20. ^ Cordell, LaDoris (2009-09-22). "Baby, You Can't Drive Your Car: A judge's favorite punishment for drivers drivers—ignition-interlock". Slate.
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  30. ^ Pamer, Melissa (28 September 2016). "Ignition Interlock Requirement for DUI Offenders Signed Into Law by Gov. Jerry Brown". KTLA 5. Retrieved 30 June 2017.
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  32. ^ Massachusetts Driver's Manual, pp. 58
  33. ^ "New Jersey Senate Bill S824". State of New Jersey, 218th Legislature. Retrieved 29 August 2019.
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  38. ^ North Carolina Driver's Manual, p. 29
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  44. ^ Motion om alkolås (in Swedish)