In 1954, an Indiana University professor and former police captain named Robert F. Borkenstein unveiled a device that would forever alter the relationship between drinking, driving, and the law. His invention, dubbed the “Breathalyzer,” was a hulking desktop machine of photometers, pistons, and chemicals. Yet, its purpose was elegantly simple: to conduct a chemical analysis on a puff of air and reveal a secret held deep within the blood.
Fast forward to today. That same analytical power now fits comfortably in your pocket. A device can, in seconds, display a number with profound legal and personal consequences. But how? How does this small, quiet object perform such a sophisticated task? It’s not magic. It’s a beautiful cascade of 19th-century physics, human physiology, and a silent, electrochemical conversation happening on a microscopic scale.
The Journey from Your Glass to Your Lungs
Before any technology can play its part, your body must first do its work. When you sip a drink, the alcohol (ethanol) embarks on a rapid journey. It bypasses the lengthy process of digestion and is absorbed directly through the lining of your stomach and small intestine into your bloodstream.
Your heart then dutifully pumps this alcohol-enriched blood to every organ and tissue, including your lungs. This is where the crucial transaction occurs. As your blood flows through the vast network of capillaries surrounding millions of tiny air sacs (the alveoli), a fundamental law of physics takes the stage: Henry’s Law.
First described by William Henry in 1803, the law states that the amount of a gas dissolved in a liquid is directly proportional to the pressure of that gas above the liquid. Think of a sealed bottle of soda. The carbon dioxide gas is forced into the liquid under high pressure. When you open it, the pressure is released, and the gas escapes.
The same principle applies in your lungs. The alcohol in your blood is volatile; it wants to escape into the air. The concentration of alcohol vapor in your alveolar air comes into direct, predictable equilibrium with the concentration of alcohol in your blood. This relationship is so consistent that science and law have codified it into a specific ratio: 2,100 to 1. This means that the amount of alcohol in 2,100 milliliters of deep-lung air is approximately the same as the amount in 1 milliliter of blood.
That puff of air you exhale is therefore not just air; it’s a gaseous snapshot of your blood. And that is what the device is waiting to read.
The Engine: A Tiny Power Plant Fueled by Alcohol
When you blow into a modern, high-quality breathalyzer, your breath sample doesn’t just hit a simple sensor. It enters an electrochemical fuel cell, a marvel of miniature engineering. To understand its function, it’s best to think of it not as a detector, but as a tiny, highly specialized power plant.
The heart of this fuel cell is a pair of platinum electrodes surrounding a porous, acid-electrolyte material. Platinum is a magnificent catalyst, meaning it can instigate a chemical reaction without being consumed by it. When the ethanol molecules from your breath pass over the surface of one electrode (the anode), the platinum mercilessly strips them of their electrons in an oxidation reaction. This process breaks the alcohol down into acetic acid, protons, and, most importantly, a stream of freed electrons.
These electrons create a tiny electrical current. The microprocessor inside the device measures the strength of this current. The more alcohol molecules present, the more electrons are liberated, and the stronger the current. This current is a direct, linear, and unambiguous signal of the alcohol concentration in the sample. The device simply translates this electrical signal into the familiar Blood Alcohol Content (BAC) number on the screen.
This is the technology inside devices like the BACtrack S80, and its elegance lies in its specificity. The platinum catalyst is uniquely tuned to react with the molecular structure of ethanol. This is profoundly important.
The Ghost in the Machine: Why Specificity is Everything
Lesser technologies, such as the semiconductor sensors found in cheaper, novelty devices, work more like a blunt instrument. They detect alcohol by measuring changes in electrical resistance when volatile organic compounds (VOCs) land on a heated tin-oxide element. The problem is that they aren’t very discerning.
To a semiconductor, other compounds can look suspiciously like ethanol. One of the most common imposters is acetone. Your body produces acetone when it burns fat for energy, a state known as ketosis. This means that someone on a strict ketogenic diet, or a person with uncontrolled diabetes, could potentially register a false positive on a semiconductor device, even if they haven’t had a single drop of alcohol.
A fuel cell, by contrast, is a chemical snob. It ignores acetone, cigarette smoke, and other VOCs. It is having a silent, electrochemical conversation exclusively with ethanol. This is the fundamental difference between a professional-grade screening tool and a keychain toy. This is why organizations like the Department of Transportation and the National Highway Traffic Safety Administration (DOT/NHTSA) approve devices that use this specific, reliable technology.
The Human Element: A Number is Not a Verdict
The journey from Borkenstein’s lumbering machine to the sleek device in your hand is a testament to technological progress. It allows us to quantify a previously subjective state with remarkable accuracy. But the science also reminds us of our own complexities. The 2,100:1 ratio is a powerful standard, but it’s a population average. An individual’s body temperature or breathing patterns can cause slight variations. The requirement to wait 20 minutes before testing isn’t arbitrary; it’s to clear residual mouth alcohol that would give a deceptively high reading.
The technology is a tool for awareness, not a license to skirt the edge. The number it displays—whether it’s 0.02%, 0.08%, or 0.15%—is the end result of a fascinating chain of events starting with a 19th-century law of physics and ending with a 21st-century electrochemical reaction. It’s a piece of data, a reflection of the silent chemistry within. The decision of what to do with that data, however, remains entirely, and soberingly, up to us.