New Year’s Eve is around the corner, and for most of us, that means a decent amount of alcohol consumption. One ever-present concern of hitting the bars is gauging whether or not you are safe to drive. If you do decide to get behind the wheel, there is the chance that you could get pulled over by the police and given the dreaded breathalyzer test. Alternatively, you might own your own breathalyzer, and rely on it to tell you if a night of imbibing has left you above or below the legal blood alcohol content (BAC).

Given that these devices can be the deciding factor between a wave goodnight from a highway patrol officer and a costly criminal offense, it’s fair to wonder how they work – and if they work.

What Breathalyzers Do

Breath alcohol testing devices were developed in the 1940s to help American police noninvasively evaluate people’s intoxication while working in the field, as taking blood or urine samples in these situations is not very convenient (or constitutional). Now used across the world, breathalyzers determine BAC by measuring the amount of ethanol in the breath. Ethanol is a very small water-soluble molecule, and as such, it readily absorbs through the tissue of the stomach into blood vessels. Because the chemical is also very volatile, when alcohol-saturated blood passes through the capillaries in the lung’s alveoli, some vaporized ethanol will diffuse into the alveolar sacs and mix into the gases in the lungs.

As you exhale into a breathalyzer, a beam of infrared radiation (IR) is passed through the air sample collection chamber. By quantifying how much of the IR hits the other side of the chamber vs how much was absorbed by the ethanol molecules, the device can calculate the concentration of ethanol per 100 mL of air. Using a set breath alcohol to blood alcohol conversion ratio of 2,100:1, the device then extrapolates the amount of ethanol in the same volume of blood and provides an immediate digital read-out.

The BAC number displayed is itself not admissible as evidence in US or UK courts, and can therefore not serve as the basis of a charge for driving while intoxicated (DWI), but the number can be used as probable cause to arrest someone and then gather more definitive evidence, i.e. a blood or urine sample. In Canada, breathalyzer readouts are admissible evidence.

In all three nations, it is illegal to operate a vehicle with a BAC of 0.08 percent (80 mg of ethanol in 100 mL of blood) or above.

There’s just one tiny problem with using portable breathalyzers for law enforcement: they aren’t accurate. Numerous peer-reviewed studies have concluded that the devices in official use have wide margins of error – often much higher than the accepted ± 0.01 percent at 0.08 percent BAC – which could falsely designate someone as over the limit or falsely reassure someone who is not fit to drive.

Worryingly, several factors can render breathalyzer readings even more inaccurate. If a person has had a sip within 15 minutes of taking a test, alcohol lingering in the mouth will inflate the BAC calculation. People with gastrointestinal reflux could also blow values higher than their true BAC, because aerosolized alcohol from their stomachs that has not yet absorbed into the bloodstream could be introduced into their breath from burping.

Individuals with diabetes often show falsely elevated values as well, because their blood contains high levels of acetone, which breathalyzer devices can confuse with ethanol.

 

Can You Trick Them?

Despite decades worth of scientific data showing the limitations of breathalyzers, police still rely on them. So, naturally, people are keen to find ways to ensure they will pass such a screening. And people being people, a lot of ridiculous methods have been suggested.

One of the most popular breathalyzer cheats involves licking or sucking on a copper coin, as this purportedly ‘neutralizes’ the alcohol in your mouth, and therefore lowers your reported BAC value. Of course, the air analyzed in one of these devices comes from your lungs, not your mouth, so removing alcohol from your mouth will not affect the results. (Even if this did work, very few coins are made of high concentrations of copper anymore.)  

Using similarly faulty logic, people have claimed that eating pungent food or mints or using mouthwash will remove or mask the alcohol in one’s system. Neither will accomplish anything, and ironically, doing the latter could inflate a BAC reading, as many types of mouthwash contain alcohol.

Eating toilet paper, clothing, or feces (not kidding) has also been recommended for those facing a breathalyzer test under less than sober circumstances. Diluting the contents of your stomach or consuming something absorbent will slow alcohol’s diffusion from the stomach to the bloodstream, but it will do nothing to change the amount of ethanol already dissolved in your blood. On top of not lowering your BAC, consuming very rough or undigestible items can cause unpleasant bowel movements at best and a potentially fatal intestinal obstruction at the worst, so please don’t do it. And we should not have to tell you that eating sh*t is a bad idea.  

According to DUI defense attorneys, many people also believe that smoking a cigarette can trick a breathalyzer. This is another tip that will backfire. When cigarettes are combusted, the sugars added to the tobacco produce a chemical called acetaldehyde. Newer breathalyzer devices, which utilize fuel cell gas sensors rather than infrared analysis, measure vaporized alcohol by detecting how much ethanol has been oxidized into acetaldehyde by an internal electrode. Add more acetaldehyde to the air in your lungs, and your reading will probably go up.

Finally, one urban myth notes that a breathalyzer can be fooled if you breathe into the mouthpiece instead of out. This will not work because these devices can tell whether or not air is being blown into them. All it will accomplish is making you look foolish and guilty.

There is, however, one technique that may actually fool the test. Per the results of multiple real-world tests, hyperventilating before blowing into a breathalyzer can lower a BAC reading enough to put someone who is just over the legal limit appear safely under it.  

This method succeeds because hyperventilating empties the lungs of residual air more than regular breathing and increases the rate at which air is replaced, leaving less time for vaporized alcohol to mix in from the capillaries. Yet to get the full effect, there are a few steps one needs to follow: after heavily hyperventilating, take a deep breath to fill up on fresh air. Then, blow forcefully but immediately begin to taper off. Stop as soon as the device beeps in completion, but before you really start to run out of air.

All breathalyzers require you to breathe continuously for several seconds before they produce a reading. They are designed to do this because the device needs that residual, deep lung air to gauge BAC, and this is only exhaled at the end of a long breath. By tapering your air quickly, you can trigger some devices to take a reading sooner (because it registers that you are nearing the end of your lung capacity) or, if the device is on a simple timer, at least trick the officer administering the test into thinking that you are doing it right.

But, this trick is no guarantee and will only reduce BAC percentage readings by around 0.014. Much like the concept of a totally reliable breathalyzer device, no foolproof means of modifying their breathalyzer results currently exists – which leads us to our last piece of advice…

Avoid Breathalyzers Altogether

If you do get pulled over after a drink or two and don’t want to put your future in the hands of unreliable technology, simply decline to take a breathalyzer test. It might make the officers suspicious, but it is entirely within your rights. You may then be asked to do a coordination test such as walking in a straight line or touching your nose. If there are grounds to take you into custody, the police will then request a blood sample for a lab-based BAC evaluation (which is accurate). You may agree to give a sample at the station or ask to be brought to a hospital to do so.  

The only way to truly prevent a DUI is to not drink and drive. And in the end, this is what we should be focused on. Because even if there were means for cheating sobriety tests, doing so would not reverse the transient mental impairment, caused by alcohol intoxication, that puts you and everyone else on the road around you in danger.