What can cause false positives on a breathalyser?

This viral video from 2019 depicting a police officer testing over the limit on a breathalyser after eating a hot cross bun has found traction again and put the spotlight on the accuracy of the devices.

Since the first breathalyser device was developed back in the 1950s the technology has remained largely unchanged. The devices aren’t foolproof by any means and law enforcement officials are well aware of this. Even if wrongful arrests or DUI convictions are rare it might benefit you to learn what types of things can trigger a false positive and what your rights are when stopped by the police.

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If law enforcement believe you are driving under the influence of alcohol or another intoxicating agent they will usually request that you perform a sobriety test, so there isn’t really too much to be concerned about unless you are incredibly uncoordinated or actually three sheets to the wind.

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HERE ARE SOME OF THE THINGS THAT CAN CAUSE A FALSE POSITIVE ON A BREATHALYSER

FOODS

Hot cross buns and other breads contain yeast which can continue to react with other ingredients baked into them forming trace amounts of alcohol which can linger in the mouth. Any baked goods made with alcohol, while they are not intoxicating, could of course produce a false positive if a reading is performed very soon after consumption.

It is not just bread that is the culprit though as pecans, macadamia nuts, ripe fruits, protein bars, energy drinks, and yet more foods will yield a positive for alcohol on a breathalyser test.

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PERSONAL HYGIENE

Smelling good isn’t a crime but liberal application of cologne or perfume can affect the accuracy of a breathalyser.

Breath freshening sprays are not the kind of thing you want to be using just as you are stopped by the police. These sprays often use alcohol as a preservative and the spray mechanism vapourizes the alcohol making it more likely to be detected by a breathalyser. It doesn’t matter how good that officer looks in their uniform, put the breath freshener down.

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The same is true for mouthwash, but if you’ve ever actually used Listerine or a similar product this is a bit of a no-brainer.

MEDICAL CONDITIONS

Medical conditions such as GERD, diabetes, hypoglycemia, or auto-brewery syndrome can also trigger a false positive.

Anyone suffering from Gastroesophageal Reflux Disease (GERD) should be aware that their condition will force stomach gasses up into the throat and mouth. Breathalysers are unsophisticated and insensitive devices that will detect any chemical substance that includes an element of the methyl group of compounds.

Auto-brewery syndrome is a rare medical condition that causes yeast in the intestines to ferment high-carbohydrate foods into alcohol. We’ve always wanted our very own brewery but this sounds like it could be uncomfortable.

Diabetics and hypoglycemia sufferers frequently have acetone on their breath, breathalysers cannot distinguish between acetone and alcohol.

FUMES

An individual that has inhaled paint, thinners, petrol or similar chemicals could also trigger a positive test. Inhaling large amounts of these is of course harmful to your health and in itself intoxicating.

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We shouldn’t need to say this but please don’t sniff petrol before driving.

ELECTRONIC INTERFERENCE

Breathalyser field units are not 100 percent accurate by the admission of those who use them and can be further thrown out by electrical interference from handheld radios, cellphones or radar devices.

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WHAT TO DO IF YOU ARE STOPPED BY POLICE

Identify the officers

SAPS and Metro Police are required to display their names clearly on their uniform. If you cannot see a name you may ask the officer to identify themselves.

Be cordial

You are not legally required to be polite to the police but it never hurts to be respectful.

If you feel unsafe

If you feel unsafe you may ask the policeman to accompany you to the nearest police station.

Breath testing

A breathalyser test will normally only be administered if the officer has good reason to believe you are driving under the influence. The test should form part of a comprehensive field sobriety test.

You may refuse the test and ask for a blood test instead but this will mean that you will need to accompany the officer to a police station to open a docket and then to a hospital to perform a test.

The handheld breathalysers used in the field are not admissible in court, however the larger Dräger test units used by law enforcement in South Africa can be used provided calibration and technician certificates are printed at the time of testing.

Don’t drive drunk

Drunk driving is dangerous regardless of whether or not you get caught and nothing outlined in this article will be of any assistance to you.

Disclaimer: This article does not serve as legal advice.