Some say that if you have had too much to drink and you get pulled over for a breathalyser test, you should suck on a copper coin. The theory is that the copper in the penny will create a chemical reaction with the alcohol in your saliva which results in an inaccurate breathalyser reading. Ironically, even the idea of a copper penny is largely a myth because most coins are made of other metals. But even the slight amount of copper within the penny cannot cause a reaction with the alcohol in your saliva. A breathalyser measures your blood alcohol content by examining the alcohol level of the air from deep within your lungs. The amount of alcohol in the air down there is actually very close to the amount of alcohol in your blood.
A penny seems to be the most commonly cited magic bullet for beating a breathalyser, but sometimes you will hear recommendations to suck on cough drops, peanuts, curry powder, onions, mouthwash or breath mints. The American TV show Mythbusters actually tested whether there were any things that you could put in your mouth or eat or suck on that would change your breathalyser test. They found that pennies, breath mints and onions did nothing to decrease the blood alcohol reading from the breathalyser, and using mouthwash actually increased the alcohol reading.
Back in the real world, one intoxicated man even thought that a mouthful of his own faeces would stump the breathalyser; his blood alcohol level was found to be twice the legal limit. We think that most people would have to be even more drunk than that to lean over, poo in their own hand and then stuff it in their mouth.
Often, the procedure for breathalyser tests is to do two of them, fifteen to twenty minutes apart. Any effects you miraculously got from what you had in your mouth the first time would need to be repeated for the second test, too. Even if you somehow managed to beat the system once, it’s less likely that you would be able to do so again. Careful studies of many samples of breath alcohol samples show that they are incredibly accurate and correlate very well with blood alcohol levels – which are unaffected by what you put in your mouth. Even faeces.