Alcohol ignition interlock

  • An alcohol interlock is a breath-testing device that is connected to the starter or ignition of a vehicle, or other on-board computer system. To start the vehicle the driver must provide a breath sample with an alcohol concentration below the pre-set limit (typically set at a value corresponding to a blood alcohol concentration of .02). Also, the driver has to provide repeated breath samples while the vehicle is in use to ensure the driver remains sober.

Anti-circumvention features

  • Anti-circumvention features prevent the alcohol interlock from being tampered with or circumvented, thus helping to ensure that the driver is unable to operate the vehicle while impaired. These features include sealed wiring, connectors, temperature and pressure gauges, driver recognition systems, and data recorders. 

Blow-and-suck method

  • The blow-and-suck method is a technique that requires the person blowing into the device to submit the sample and briefly suck air back after having provided the sample. The purpose of this exercise is to demonstrate that an individual is actually providing the breath sample and that it is not coming from a non-human source and to reduce the likelihood of an – untrained – bystander providing the breath sample in place of the offender.


  • Breath alcohol concentration (BrAC) is used to extrapolate or estimate an individual’s blood alcohol content when providing a breath sample. It is a surrogate measure for the blood alcohol concentration (BAC) and provides a measure of the amount of alcohol a person has consumed.

BrAC threshold

  • The BrAC threshold is the pre-set limit at which a warning or a permanent lock-out of the vehicle can occur. Typically the BrAC threshold is set at a value corresponding to a blood alcohol concentration of .02 and may vary up to .05 according to the requirements of individual jurisdictions.

Breath pulse code

  • The breath pulse code is a technique that requires a series of short and long breath pulses which must be provided prior to giving a breath sample. Requiring the use of such codes when providing a breath sample reduces the likelihood of an – untrained – bystander providing the breath sample in place of the offender. Also, associating such codes with high-BrAC readings can be useful in identifying the driver in some instances. 

Breath volume

  • The breath volume is the volume of air the interlock requires to complete an acceptable breath test. The breath volume minimum standard is 1.5 liters of alveolar air in the United States.

Certificate of installation

  • The certificate of installation is issued by the service provider to the offender. This certificate contains essential information relating to the service provider, the vehicle, and the device that was installed. At the very least, the certificate of installation must contain the date of the installation, the name and address of the alcohol interlock provider, and the name of the technician that installed the device. It must also ensure that the alcohol interlock is installed on the correct vehicle, which is confirmed by listing the vehicle registration number, the year, make and model of the vehicle, and the vehicle identification number. The certificate must also record the serial number of the alcohol interlock device.

Data recorder

  • The data recorder is a component of the interlock device that records and captures the date and time of all initial breath tests and running retests, any attempts to start the vehicle, and any attempts to tamper with or circumvent the device. It also records breath sample violations, lockouts resulting from positive breath alcohol readings, and the activation of the emergency override feature. By keeping such a detailed registry of events, the data recorder creates a record and timeline of any and all uses of the interlocked vehicle which can then be reviewed and assessed by courts, probation, treatment or licensing professionals.

Detachable handset

  • A detachable handset is a feature of some alcohol interlocks, which allows the interlock to warm up at room temperature before being transported from a residence to the vehicle. The handset uses wireless technology that can mitigate the influence that cold temperatures may have on this device (e.g., shorter warm-up time). This technology requires that the handset must be 164 feet or 50 meters from the vehicle.

Electrochemical sensor (fuel cell)

  • The electrochemical sensor or fuel cell is the most common sensor technology used in modern alcohol interlocks and other breath testing devices. In these devices, the alcohol in the breath sample undergoes a chemical oxidation reaction when it comes into contact with a platinum disc. The electrical response (current) that is generated is converted into an alcohol reading which is compared to a baseline (non-alcohol) reading. The change in the magnitude of the current is proportional to the amount of alcohol contained in the breath sample.

Emergency override

  • The emergency override is a standard feature of most alcohol interlocks which allows the driver to override the system in the event of an emergency. The emergency override feature will allow the driver of the vehicle to override the ignition interlock and avoid providing a breath sample before starting the vehicle one time only. Use of this feature will be captured by the data recorder.

False positive

  • A false positive occurs when the alcohol concentration in the body of the person delivering the breath sample is truly below the pre-set limit, but the device erroneously records it as if the person was above the pre-set limit. This can happen, for example, due to mouth alcohol, when the person delivering the breath sample recently drank alcohol or used mouth wash containing alcohol and did not rinse before blowing into the device.

Hum-tone recognition

  • Hum-tone recognition is a technique that requires a driver to hum while providing a breath sample. It is difficult to master without proper training from the service providers. This can greatly limit opportunities for an inexperienced user or bystander to provide an acceptable sample without several repeated failed attempts that would result in a lock-out of the vehicle.

Infrared sensor

  • An infrared sensor uses several optical filters designed specifically to measure alcohol. Alcohol in the breath sample is measured by passing a narrow band of infrared light through one side of a breath sample chamber and detecting emergent light on the other side. The alcohol concentration in a breath sample is measured by the amount of the infrared light absorbed. This technology is not currently available in alcohol interlock devices due to the large size of the sensor.

Infrared spectroscopy

  • Infrared spectroscopy is a technology that can be used to detect alcohol and metabolized alcohol bi-products. Specifically, tissue spectroscopy estimates BrAC levels by measuring how much light has been absorbed at particular wavelengths from a beam of near-infrared light reflected from the tissue of the driver.

 Lock-out time

  • Lock-out time refers to the period of time following a failed BrAC test during which a subsequent test may not be taken. Once the lock-out time has ended, the driver may make another attempt to start the vehicle. The typical timeframe for the lock-out period is a short duration of five minutes after one failed attempt or a false positive. After a first short lock-out, the device may go into long lock-out mode (e.g., 20 minutes) in case the second breath test after the short lock-out is failed as well.

Mouth alcohol

  • Mouth alcohol is residual alcohol in the mouth that is present immediately following the consumption of some foods, beverages, medicine, or mouth spray. Mouth alcohol will typically dissipate within five to ten minutes. Mouth alcohol will trigger a positive reading and a lock out of the vehicle, even when the true alcohol concentration in the body of the person delivering the breath sample is below the pre-set limit.

Photo recognition

  • Photo recognition is used by interlock devices with a camera and captures an image of the driver before the breath sample is provided, while the breath sample is delivered, and after the breath sample has registered. This feature may allow courts more confidence in determining who is driving the motor vehicle and providing breath samples while the vehicle is in operation. To date, this feature is not widely available.

Pull over notice

  • Pull over notice refers to the time available following a failed BrAC retest to pull over and stop the vehicle before the alarm/horn and/or flashing light sanction is activated. The pull over notice time period is typically three minutes during which a driver is expected to pull over and provide a breath sample. If the driver has not complied with these instructions after the initial three minute period, an additional three minute period is given before an alarm is activated. If the driver still has not provided an acceptable breath sample, a violation is recorded and the offender will be called in to the service center. If the offender neglects to go to the service center within a couple of days, the vehicle will be locked out permanently.


  • Recalibration is the process necessary to ensure the interlock device measures accurately. This is done by comparing the measurement output of an instrument to a standard having known measurement characteristics. An alcohol interlock should be brought back to the service provider for recalibration every ­­­90 days, on average, although this may vary according to the type of sensor used.

Recall notice

  • A recall notice warns the driver that, after a specific time period, there will be a permanent lockout of the vehicle and the driver will not be able start the vehicle. The driver can avoid the permanent lock out by bringing the vehicle to the service center for servicing. The notice is likely to occur if the driver accumulates a certain number of violations within a given period, activates the emergency override, or if the device needs to be calibrated.

Running re-test

  • The running re-test is also known as rolling retest; it is a feature requiring a repeated breath test that the driver must continue to perform at random intervals once the vehicle has been successfully started. The purpose of the running re-test is to prevent the driver from drinking once the vehicle has started and the engine is idling, and to detect a rising BrAC level in the driver once the vehicle has been started.

Sealed wiring

  • Sealed wiring refers to special tape wrapped around all wiring and circuits of the alcohol interlock device to seal them and protect them from attempts to tamper with the device. Any removal or destruction of this tape provides clear evidence of an attempt to tamper with the alcohol interlock device.

Semiconductor sensor

  • A semiconductor sensor is a sensor containing a small bead of metal oxide that is heated to a very high temperature. Power is then applied to the sensor, and the current generated using a non-alcohol breath sample is measured to form a baseline reading. When an alcohol-positive breath sample is given, the device detects the alcohol by measuring the change in the electrical current generated by the alcohol positive sample and comparing it to the current generated by the baseline sample. The measured change in the electrical current (resistance) can be converted into a breath alcohol reading.

Stall protection time

  • Stall protection time is the amount of time available to restart the vehicle after it has been turned off or stalled without having to provide a new breath test (e.g., if the vehicle stalls at an intersection). The stall protection time period ranges from one to five minutes with three minutes being the average length of time.

Technical standards

  • Technical standards are guidelines that specify the performance of the alcohol interlock device under various conditions and in different jurisdictions. Technical standards have been implemented in several countries including the United States (these guidelines have been developed by NHTSA), Canada, the European Union, and Australia. Several of these guidelines have been updated recently.

Temperature and pressure gauges

  • These gauges are constructed with several layers of security, meaning that a breath sample must satisfy several criteria before being accepted as a valid sample and the power to the starter system is released. These layers may include temperature, pressure, duration and/or volume, moisture, and alcohol content of a breath sample. These gauges were developed as anti-circumvention features to detect non-human breath samples.

Transdermal analysis

  • Transdermal analysis measures alcohol excreted through skin in the form of vaporous perspiration. Since BAC is correlated with the alcohol concentration in sweat, wireless, body-worn devices have been created to continuously measure the perspiration to detect alcohol in the body. The device stores data with time stamps and transmits the data to be downloaded on to a monitoring center.

Vehicle-based impairment detection

  • Vehicle-based impairment detection is a technology that involves the use of multiple sensors in a vehicle connected to a neural network or another impairment detection algorithm. In simple terms, the device consists of sensor systems within a vehicle that measures certain elements or types of behavior, such as impairment due to alcohol use or fatigue.


  • A violation primarily pertains to providing a breath sample that is over the pre-set limit. Other kinds of violations may be defined in the program rules set out by the jurisdiction (e.g., driving during a specific time period). If a violation occurs the vehicle will not start and the data recorder will record it.

Warm-up time

  • Warm-up time is the period in which the driver must wait until the device warms up before delivering a breath sample. The duration of the warm-up time typically spans from several seconds to several minutes depending on various environmental and climatic influences.