Tips To Avoid Failed Or Positive Interlock Readings (Even If You Haven’t Been Drinking)
Unexpected interlock readings can be frustrating, especially when you haven’t had a drink and you’re doing everything right. Yet many drivers are surprised by how easily everyday habits, products, and routines can trigger a failed or positive result.
Understanding why these readings occur, and what your device is actually detecting, is the key to staying compliant and avoiding unnecessary lockouts, violations, or program extensions. With a few simple adjustments, you can take control of your interlock experience and prevent issues before they happen.
With that being said, we’ve broken down the most common causes of false positives, usually caused by mouth alcohol, and the practical steps that you can take to keep your alcohol interlock program running smoothly.
Why Alcohol Interlock Devices Can Produce Unexpected Readings
Understanding why an interlock might register alcohol when you haven’t been drinking starts with how the device measures your breath. Alcohol interlock systems use fuel-cell sensors, which react to the presence of alcohol molecules and convert that reaction into a reading. These sensors are highly sensitive, designed to detect even trace levels, so they can sometimes respond to airborne substances or contaminants that aren’t related to alcoholic drinks.
It’s also common for people to misunderstand what breathalysers can and can’t pick up, which leads to myths about accuracy or reliability. In most cases, unexpected results are linked to how the device is used. Taking the time to follow proper warm-up steps and the correct breathing technique can make readings far more consistent and dependable.
Everyday Products That Can Trigger A Failed Or Positive Reading
Mouthwash, Breath Fresheners & Oral Hygiene Products
Many mouthwashes, mints, and breath sprays contain high-percentage alcohol that stays in the mouth long after use. Even tiny traces can register as a strong reading because the sensor detects mouth alcohol more intensely than deep-lung breath. Products labelled “alcohol-free” tend to reduce this issue, but anything used moments before a test can still leave detectable residue.
Foods & Drinks That Ferment In The Mouth
Certain foods naturally produce alcohol as they break down; ripe fruit, kombucha, vinegar-based meals, and even hot cross buns can momentarily spike oral alcohol levels. Coffee mixed with sugary foods can also ferment briefly if particles remain on the teeth. This temporary fermentation is enough to create a short-lived positive reading during a breath sample.
Medication, Inhalers & Medical Conditions
Some asthma inhalers, cough syrups, and liquid medications contain alcohol-based compounds that can register during a breath test. Medical conditions such as diabetes may also influence readings because ketones can convert into acetone-type vapours. When symptoms, medications, or treatment plans affect breathing patterns, supervised testing or medical documentation may be needed to explain irregular results.
Hand Sanitisers & Household Cleaning Products
Alcohol vapours from hand sanitiser, disinfectant sprays, or cleaning products can linger in the air or on your hands. When these vapours are inhaled or remain present inside the vehicle, they can enter the breath sample and momentarily affect the reading. Even small airborne residues from cleaning surfaces or using sanitiser inside the cabin can be detected by the interlock device.
How To Prepare Before Every Interlock Test To Avoid False Positives
Rinse & Clean Your Mouth
A quick water rinse helps clear lingering flavours, strong odours, or residue that may interfere with your next reading. Give yourself a moment after brushing your teeth or using breath products so the device receives a clean, uncontaminated sample.
Avoid Eating Or Drinking 10–15 Minutes Before Starting The Car
Food particles, sugary drinks, and even flavoured beverages can leave trace residues in the mouth. Allowing time for your mouth to settle ensures the sample reflects your actual breath rather than leftover digestion.
Ensure The Car Cabin Is Free From Alcohol Vapours
Cleaning sprays, perfume, sanitiser, or recently spilled products can release vapours into the air. Keep windows open briefly if needed so the cabin has fresh airflow.
Follow Correct Breathing Technique
Use a slow, steady breath as recommended by Guardian Interlock. Rushed breaths or inconsistent airflow can cause errors or force a retest, making your trip more stressful than it needs to be.
Environmental Factors That Can Lead To Failed Tests
Temperature & Moisture
Cold mornings, high humidity, and condensation inside the handset can temporarily affect how the interlock analyses your breath sample. These conditions may cause the device to take longer to stabilise or produce errors while it adjusts. Giving the unit extra warm-up time, especially in winter or after rain, helps ensure it’s ready for an accurate reading.
Fuel, Paint & Chemical Fumes
Interlocks can detect strong vapours in enclosed or poorly ventilated spaces. Working near fuel, paint thinners, solvents, or heavy chemical fumes, which are common around workshops or garages, may disrupt the sensor. If possible, move the vehicle into fresh air or increase ventilation before attempting a test to minimise interference.
What To Do If You Receive A Failed Or Positive Reading
Stay Calm & Wait Before Retesting
If your interlock records a failed or positive reading, pause and let the system guide you through its timed retest process. Avoid blowing again immediately, as rapid repeat attempts can trap residual particles or vapours and lead to further inconsistent results. Giving the device time helps ensure the next sample is clean and reliable.
Document Everything (Especially If You Were Sober)
Write down anything that could have contributed: foods you ate, products you used, medications taken, or any environmental exposure such as sanitiser or cleaning sprays. This record becomes valuable if you’re later asked to explain a reading, helping show patterns or possible causes unrelated to drinking.
Contact Guardian Interlock If Issues Persist
If you continue receiving unexpected readings, reach out to our team at Guardian Interlock for support. Technicians can run diagnostics, check calibration, and identify whether sensor or device issues may be contributing. Early communication helps resolve problems quickly and protects your program compliance.
Reach Out To Guardian Interlock For Support Today!
Managing an alcohol interlock program can feel overwhelming at times, but you don’t need to navigate it alone. If you’re unsure about a reading, need help understanding your device, or want guidance throughout your program, our team is here to support you at every step.
Email admin@guardianinterlock.com.au or call 1300 881 005 today. Our support team is ready to assist you.
