Questions & Answers

a) How does the alcohol interlock work and how is it installed?
b) What technologies are used in alcohol interlocks to detect alcohol in breath samples?
  How accurate are alcohol interlocks in detecting alcohol?
  Are there technical standards established for alcohol interlocks?
a) How does mouth alcohol affect the alcohol interlock device?
b) How do temperature and altitude (elevation) affect the performance of the alcohol interlock?
c) What is the expected warm-up time for an alcohol interlock?
a) What programmable features are provided with the alcohol interlock?
b) Who is responsible for programming the alcohol interlock device?
  Which anti-circumvention features are included with the alcohol interlock?
  What is a running retest?
  What is the emergency override feature, and how does it work?
  What types of alcohol interlock technology are being considered for future use?

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1a) How does the alcohol interlock work and how is it installed?

  • The alcohol interlock device is connected to the starter or ignition, or other on-board computer system of a vehicle. To start the vehicle the driver must provide a breath sample with an alcohol concentration below a specific pre-set limit (usually corresponding to blood alcohol concentration of .02). If an alcohol concentration above this limit is detected the vehicle will not start.

  • Once a breath sample has been provided, if the amount of alcohol in the breath sample exceeds .02, the alcohol interlock interrupts the flow of power between the vehicle ignition switch and the starter system of the engine.

  • If an acceptable breath sample is given, the alcohol interlock closes the open circuit and permits power to reach the starter system so that the engine can start.

  • It is important to note that the alcohol interlock is connected to the starter system of a vehicle and not to the engine, and therefore, will not affect a running engine.

  • The installation of the alcohol interlock on most vehicles is relatively simple and takes between 45 minutes and two hours depending on the sophistication of the vehicle and the experience of the installer. Generally, most installations require about 45 minutes and should always be completed by a licensed, professional installer.

  • One hour or more may be required to install an interlock on a high-end vehicle with a sophisticated electronics system. Manufacturers of these vehicles are also reluctant to make schematics readily available online to installers which might require offenders to have a wiring harness installed to allow for easier installation.

  • During the installation process, offenders receive information about the alcohol interlock and learn how to blow into the device to provide a breath sample. Offenders are also provided with a certificate of installation to submit to the licensing or monitoring authority as proof of device installation.

1b) What technologies are used in alcohol interlocks to detect alcohol in breath samples?

  • There are three types of sensors that are used in alcohol interlock devices: semiconductor, electrochemical (fuel cell), and infrared.

  • Semiconductor technology is less expensive compared to both fuel cells and infrared technology, but this sensor is not ethyl alcohol-specific (i.e., a positive alcohol reading can be triggered by other substances such as perfume or cigarette smoke), resulting in frequent false positive tests. These devices also require maintenance more often (every 30 days) to maintain the accuracy of the alcohol interlock. Most jurisdictions have elected to move away from this less advanced technology.

  • Electrochemical sensors address the two shortcomings of semiconductor sensors: they ensure that positive alcohol readings are the result of alcohol in the breath of drivers (ethyl alcohol-specific) and require less frequent calibration (e.g., once every several months). While fuel cell technology is slightly more expensive than semiconductor technology, it is much more accurate and reliable.

  • Infrared technology has greater long-term calibration stability compared to fuel cell and semiconductor technology and is commonly used for evidential breath testing. However, this technology is impractical for alcohol interlock devices due to its large size. Moreover, this technology is quite expensive and there is a high level of difficulty associated with achieving specificity and accuracy at low BAC levels.

2) How accurate are alcohol interlocks in detecting alcohol?

  • Alcohol interlocks containing an electrochemical sensor are accurate in detecting alcohol consumption 99% of the time.

  • According to NHTSA model specifications (which currently under revision) these devices must meet specific accuracy requirements. The NHTSA specifications require that vehicles equipped with alcohol interlocks with a .02 pre-set limit must be prevented from starting under extreme conditions 98% of the time when a breath sample registers at least .065 (Beirness 2001).

  • It must be noted that the primary purpose of the alcohol interlock is to prevent an impaired driver from operating a motor vehicle (to accurately detect alcohol), and to prevent circumvention and tampering. The objective of the device is not to provide drivers with a precise measurement of their breath alcohol content (although the accuracy of the breath alcohol measurement with an electrochemical sensor is close (but not comparable) to an evidential level).

3) Are there technical standards established for alcohol interlocks?

  • Technical standards established for alcohol interlocks vary across jurisdictions and according to the intended purpose of the device (i.e., monitoring impaired driving offenders vs. monitoring commercial drivers). Technical standards currently exist in the United States, Canada, the EU, and Australia.

  • In North America, alcohol interlocks are primarily installed in private vehicles with the intention of monitoring impaired driving offenders. In the European Union (EU), alcohol interlocks have also been installed in commercial vehicles (e.g., buses, taxis, heavy trucks).

  • NHTSA developed model specifications in 1992 and these are currently under revision. These guidelines mandate certain criteria for alcohol interlock devices, such as anti-circumvention features and pre-set values. As part of the revisions, it has been proposed that NHTSA create a conforming products list for those devices that meet all of the model specifications.

  • Many jurisdictions in the U.S. further require devices and/or manufacturers to be certified by the state as demonstration that the device meets necessary technical requirements and is approved for use in the state. 

  • A revised technical standard has recently been implemented in Canada, and in 2007, the EU updated their technical standard (created by the CENELEC committee) which is the most contemporary, comprehensive, rigorous, and high-quality standard available at this time. Australia has also established a technical standard that emphasizes accurate and reliable measurement of alcohol.  

  • These initiatives to update technical standards reflect technological advances and design improvements. The goal of a technical standard is to ensure a uniform standard for devices, consistent quality, and efficacy in these devices.

4a) How does mouth alcohol affect the alcohol interlock device?

  • If alcohol from recent consumption of food, drink, mouth spray, or medicine is present in the mouth or throat at the time that a breath sample is being delivered, an elevated alcohol concentration will be detected and the alcohol interlock will likely prevent the vehicle from starting.

  • Drivers are advised not to consume anything containing alcohol within the five minutes prior to providing a breath sample.  

  • Residual mouth alcohol will dissipate within a few minutes of consumption as it is taken up by saliva or absorbed into the body.

  • If taking medication, users should note whether or not it contains alcohol because if the sample registers a BrAC above the pre-set limit the interlock will prevent the vehicle from starting and a breath test violation will be recorded.

  • It is important that service center technicians educate offenders about mouth alcohol at the time of device installation.

4b) How do temperature and altitude (elevation) affect the performance of the alcohol interlock?

  • The National Highway Traffic Safety Administration (NHTSA) recognizes that many jurisdictions are subject to extreme temperature and other conditions.

  • Generally, extreme temperatures and altitude levels have nominal effects on alcohol interlocks. These devices are designed to withstand adverse effects of temperature and elevation similar to all other technologies that are a regular part of vehicle design.

  • Most interlocks can withstand temperatures ranging from -49 to +185 degrees Fahrenheit (-45 to +85 degrees Celsius) and altitudes of up to 11,482 feet (3,500 meters) (Burger 2001 cited in Bax et al. 2001).

  • Extreme temperatures and altitude will not affect the functioning of an alcohol interlock, with the exception of a five minute warm-up time in extreme cold temperatures.

4c) What is the expected warm-up time for an alcohol interlock?

  • The duration of the warm-up time typically spans from several seconds to several minutes at very low temperatures.

  • While warm-up time is an inherent feature of the alcohol interlock (similar to a photocopier), it nonetheless can cause inconvenience and frustration for drivers in extreme temperatures (Beirness et al. 2007).

  • Technological advances have reduced the warm-up period. For example, the wireless alcohol interlock allows drivers to provide a breath sample from inside the home a few minutes before entering the vehicle. The handset of the device would be with the driver and not in the vehicle, and thus, would be warm. This option is particularly useful in extremely cold climates. Wireless communication occurs between a handset and a control unit that are up to 50 meters apart.

  • However, the wireless device does increase the opportunity for someone other than the driver to deliver the breath sample. For this reason, the European Standard for these devices (EN 50436-2) requires that wireless communication occur between the handset and the control unit within 30 seconds of the analysis of the breath sample.

5a) What programmable features are provided with the alcohol interlock?

  • Alcohol interlocks have a wide range of programmable features which allows manufacturers to customize the devices to meet requirements in different jurisdictions. Some of the features that are available with most alcohol interlock devices include: language and visual display, pre-set limit or BrAC threshold, lock-out time, stall protection time, pull over notice, recall notice, and breath volume.

  • There are also several new features not available on some devices that improve the ability of authorities to monitor interlock offenders. These emerging features include: GPS, real-time reporting, video streaming, and 911 notification. Essentially, these features allow monitoring authorities to locate and track interlock offenders and also be alerted of the occurrence of violations as they happen. These features are a useful option as a graduated sanction for offenders who are consistently non-compliant.

5b) Who is responsible for programming the alcohol interlock device?

  • In some states, the Department of Motor Vehicles (DMV or its equivalent) certifies the alcohol interlock and ensures that the manufacturer makes specific features operational, as required by state regulations.

  • The DMV may also conduct routine and random inspections of service centers to ensure quality control of alcohol interlock devices and programmable features.

  • Other state agencies such as the Department of Transportation or the Department of Corrections may also be given the authority to certify devices and institute vendor oversight protocols.

  • In other states, service providers may be responsible for ensuring the required features are operational. Under these circumstances, it is important that the state closely monitor service providers to ensure that all devices are programmed to meet the necessary requirements.

6) Which anti-circumvention features are included with the alcohol interlock?

  • Earlier versions of alcohol interlocks could be easily bypassed due to their limited anti-circumvention features. For example, alcohol interlocks were not equipped with features that could detect and/or prevent a bystander from providing a breath sample on behalf of a driver, or detect the substitution of stored air samples (e.g., from an air tank or balloon).

  • Modern alcohol interlock devices have largely overcome these limitations with the inclusion of sophisticated, effective anti-circumvention features that are mandated by the U.S. model specifications (National Highway Traffic Safety Administration 1992).

  • Anti-circumvention features include sealed wiring, connectors (e.g., soldered wires, T-Taps, Scotch locks, barrel or butt connectors), temperature and pressure gauges, driver recognition systems (e.g., breath pulse codes, hum-tone recognition, photo recognition), and the data recorder.

  • The data recorder captures the date and time of all initial breath tests and running re-tests, any attempts to start the vehicle, and any attempts to tamper with or circumvent the device. It also records breath sample violations, lock-outs resulting from positive breath alcohol readings, and the activation of the emergency override feature.

7) What is a running retest?

  • A running re-test is a random, repeated breath test that drivers must continue to provide once the vehicle has been successfully started. The first re-test generally occurs within 5-15 minutes after the vehicle has been started.  

  • The purpose of the running re-test is to prevent drivers from drinking once the vehicle has been started and the engine is idling, and to detect a rising BrAC level in drivers once the vehicle has been started.

  • This feature reduces the likelihood of a bystander providing a breath sample to start the vehicle in that to continue driving the driver must repeatedly provide alcohol-free breath samples when prompted to do so.  

  • If drivers do not provide a running re-test or fail, an auditory or visual warning (e.g., alarm, flashing lights) will persist until the vehicle is turned off ensuring detection.

  • At no point will the alcohol interlock shut off the engine and create a traffic hazard (Beirness 2001).

  • There has been some concern raised regarding the safety of performing a running re-test while the vehicle is in motion. However, the running re-test prompt allows sufficient time for drivers to pull over at the side of the road in a safe location, or wait until stopped at a red light.

  • A study by Medeiros-Ward and Strayer (2011) found that the mental workload of texting was more demanding than the mental workload needed to perform a running re-test.

8) What is the emergency override feature, and how does it work?

  • The emergency override is a feature available on some alcohol interlocks. The feature will allow drivers to override the alcohol interlock and avoid providing a breath sample before starting the vehicle one time only.  

  • The availability of the override feature is contingent on approval from the program administrator. For instance, jurisdictions such as Florida and Quebec permit the override feature, whereas jurisdictions such as Pennsylvania and Ontario do not (Robertson et al. 2006).

  • This feature allows the vehicle to be used in emergency situations during which the use of the vehicle is necessary or to allow another person not familiar with the device to start the vehicle (Beirness and Boase 2007).

  • Some concerns have been raised regarding the potential for this feature to allow an intoxicated individual to operate a vehicle and the liability this may create.

  • If the use of this feature is permitted, it is important that the activation of the override be recorded by the data recorder and that a record of the usage of the vehicle during this period is captured.

  • To prevent misuse of this feature, program administrators can require servicing following each use of the feature, or require servicing within a restricted time period.

9) What types of alcohol interlock technology are being considered for future use?

  • In recent years, there has been some discussion regarding the installation of alcohol interlocks as a standard feature on all motor vehicles.

  • The current technology is designed primarily for offenders and professional applications and will likely be less appropriate for private citizens. For this reason, efforts are underway to develop unobtrusive methods for detecting alcohol consumption by drivers. 

  • To increase acceptance of and compliance with the use of alcohol interlocks in all vehicles, several criteria must be met. The devices must be fast, accurate, reliable, and repeatable. They cannot impede or interfere with a vehicle from starting or being started if the driver is not alcohol impaired. They must also be functional across a wide range of driving and environmental conditions, require little or no maintenance, and be tamper/circumvention resistant. Finally, the devices must also be entirely transparent and undetectable to the sober driver (DADSS 2012).

  • The DADSS project is an initiative that seeks to research, develop, and pilot non-invasive in-vehicle alcohol detection technologies that quickly and accurately measure a driver’s BAC. Two specific approaches were chosen for further investigation and development: tissue spectroscopy (touch-based sensors) and offset spectroscopy (breath-based sensors). It should be noted however, that this technology is still several years away from being fully developed.

  • There are also alternatives to the use of alcohol detection devices in vehicles including transdermal and in-home monitoring. They can also be applied as a graduated sanction for those offenders who demonstrate consistent non-compliance with interlock program requirements.

Last updated November 2012