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A few years ago, a client claimed to have beaten the evidential breath test machine (EBM) some years before by sucking a penny. It’s an old urban legend that the copper in the coin will interfere with the EBM’s ability to detect alcohol, but is it true?

To answer that we need to understand how the EBM works. There are a few types of EBM used in the UK. They all use an infra-red detector to look for alcohol. Devices like the Lion Intoxilyzer then use the findings of the infra-red sensor to produce a result. More sophisticated devices like the Intoximeter use the infra-red sensor to work out when the subject is blowing air from the deepest part of their lungs then transfers a small portion of the sample into a fuel cell for further analysis.

Infra-red detection is achieved by saturating a sensor with non-dispersive infra-red light. As air passes between the light source and the sensor a computer analyses how much light is collected and uses that information to work out how much light has been dispersed by the chemicals in the air passing in front of the sensor. For that the computer can calculate a) the chemical composition of the air; and b) how much of it is alcohol.

The fuel cell design uses its infra-red detectors to establish whether alcohol is present or not. They then look for a plateau in the amount of alcohol being exhaled before drawing a tiny portion of the air into the fuel cell where one portion is oxidised (i.e. it releases electrons) and the other is reduced (i.e. it absorbs electrons). If alcohol is present, then an ammeter connected to electrodes will measure a current. The electrical current detected is equal to the alcohol concentration present in the sample.

Both systems are able to detect the difference between different chemicals including different types of alcohol. This is because different chemicals will disperse infra-red light differently to the ethanol that EBMs look for and so will not fool the machines.

It’s also been claimed that sucking a penny causes you to produce saliva that interferes with the machine. It is possible that if you introduced saliva into the machine it would fail to operate and would return an error message; however, you would also be likely to be charged with failing to provide as you would have to spit into the machine, which would be fairly obvious to the police officer.

So, in conclusion you cannot fool a breath test machine by sucking a penny. How did our client get away with it? Our best guesses are: a) it was such a long time ago the machine was an older version that was not as sophisticated as the modern ones; b) he has misremembered how much he drank over the years, building it up in his memory; c) he got lucky and the machine happened to be broken.

One other important point to consider is that if the police discovered you were sucking a penny, they might well decide to charge you with attempting to pervert the course of justice, which is far more serious than drink driving.

If you are charged with drink driving it is often worth the effort of checking how the police officer conducted the breath test procedure to establish that all the appropriate warnings and instructions were given. Such challenges are far more likely to be successful than sucking a penny. If you need help with a drink driving allegation, please feel free to call us on 020 8242 4440 or email us via our contact page.