How alcohol interlock devices work

An alcohol interlock is a breathalyser or a device used for breath testing that is connected to a vehicle’s ignition circuit. It is used for measuring the driver’s BAC (breath alcohol level) before the driver starts the vehicle. Interlock devices are actually incapacitators.

The device will inhibit a driver’s inclination to drive while being drunk beyond the legal limit and will not allow him or her to do so. The device therefore very effectively prevents people from driving after drinking alcohol. This reduces the incidence of accidents as well as amplifies road safety.


How an alcohol interlock device works

A driver is required to blow into the interlock equipment for a few seconds before starting the vehicle and the device will generate a reading indicating the driver’s BAC level. If the reading exceeds the legal limit then the driver will not be allowed to start the vehicle.

On the mandatory scheme, the drivers must have a BAC of zero and if the driver is found to have exceeded this range, then the alcohol interlock will not allow the vehicle to be started for at least 5-30 minutes so that any severe situation is prevented.

After three minutes have elapsed, the device will ask the driver to conduct another breath test and then the vehicle can be re-started. If the vehicle has been stalled and restarted immediately, then a fresh test isn’t required.

Additionally, alcohol interlock devices require drivers to undergo re-tests at regular yet random intervals while driving. The driver will have to blow into the device again. A period of approximately 3 minutes is provided to the driver for conducting a retest and the vehicle will remain motionless. If the readings indicate a lower range still, then the driver can continue to drive. This feature is also known as a “rolling retest”.

If a breath sample is not provided or the retest shows a higher BAC reading, the interlock device will automatically raise an alarm in the form of a honk of the horn and flashing the headlights. This will continue until a successful retest is conducted.

All the activities of this device is monitored by a built-in data logger. It records every incident that the device experiences while the vehicle is moving. This information can then be used by the Registrar of Motor Vehicles for observational purposes. The participants who fail the breath tests on a regular basis will be sent a written letter by the Registrar. Any participant who commits more than one limit exceeding incidents during the final 3 month period of alcohol interlock installation will be given an extension in the period of using this device.


Learning to use an alcohol interlock device

Alcohol interlock installation into your vehicle is performed by experienced installers who will also provide extensive and comprehensive training to the participants regarding its proper usage and maintenance. This training involves a demonstration of the device’s usage followed by personal depiction by the installers. The participant’s spouse, partner or other family members can also receive training at the time of installation. Proper training in this regard is extremely critical otherwise you will not be aware about the correct way of blowing or following the instructions of the device, which can cause trouble and even can risk your life.


How to maintain an alcohol interlock

Alcohol interlock is a device that, like any other equipment or machinery, requires proper and regular maintenance. For this purpose, drivers need to consult the installation facility at least once every month because the device can be serviced and calibrated by them only. While maintenance is being performed, the device’s functioning will also be checked and the previous month’s information recorded by its data-logger will be downloaded and sent to the Registrar.

A visual inspection will also be performed by the approved installer along with the vehicle and the wiring used for connecting the device to the ignition circuit. This is done to ensure that no tampering has been made or circumvention has occurred from the participant’s side.

If you do not bring the device for servicing then there is a probability that it may lock itself and when this happens, the vehicle will not start unless the device is reset by the installer. The vehicle will have to be towed to the nearest provider of the device or in emergency situations, the provider will have to visit the vehicle to remotely reset the device. All costs involved in this process will be the responsibility of the participant and a call-out fee will be charged. This incident will also be reported to the Registrar of Motor Vehicles.


Can you override the alcohol interlock?

It is not possible to tamper with the interlock because the approved installer will check the device at regular intervals and will immediately detect if it has been tampered with. The device will also be equipped with built-in anti-circumvention features including tamper-proof seals that cover all its connections and are inspected at each service.

Its control module is connected to the vehicle permanently which ensures thorough recording of all events even when the power supply to the unit is interrupted. Explanation regarding recorded events will be required from the participant. Its sensory mechanism has been designed in a way that it rejects bogus samples and also ensures that unfiltered and undisguised human breath is blown for the analysis. Inhibiting “curbside” facilitated starts, for instance drinking while you drive and consuming alcohol while the vehicle is turned on, can be easily detected by the installer by running random re-tests on the device during servicing.


What are the consequences?

Any failure in compliance with the interlock device usage terms and conditions including the tampering of the device will make the participant an offender by law and this entails a penalty fee of around $2,500. Assisting the participant in interfering with the alcohol interlock is also an offence and its maximum penalty is $2,500 as well.


Is there any suitable alternative to alcohol interlocks?

Installing an alcohol interlock is not mandatory for every person but it is a rule that to reclaim a driver’s license of any class, it is compulsory to install it in the vehicle for a pre-determined period of time.

If you’d like more information on alcohol interlock devices, or would just like to find out more about breathalysers, contact us and we’ll be happy to help you out.


Christina Cini

Christina Cini

Christina is our very skilled Quality Assurance Manager/ Technician. With her degree in Mechatronics Engineering, she is able to apply her field of studies to her current occupation, also providing a better understanding into our more technical blog posts such as calibration, maintenance of your breathalyser, as well as sensors.


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