Alcohol exits the body in different ways. The vast majority is metabolized in the body and exits as carbon dioxide and water. Much smaller amounts of alcohol are eliminated through excretion in the urine, through the skin as perspiration, in saliva or exhaled in the breath.
A portable breathalyzer samples and measures alcohol exhaled in the breath while a SCRAM ankle bracelet samples alcohol excreted through the skin. Alcohol exhaled through the breath is measured as Breath Alcohol Content (commonly BAC or BrAC) while TAC has been coined to mean transdermal alcohol content (through the skin).
Law Enforcement breathalyzers, the better personal breathalyzers and SCRAM all use precision fuel cell technology to detect and measure alcohol content.
In a fuel cell device the sample is directed into a specially constructed chamber where the alcohol is chemically oxidized and generates electrical current. The higher the alcohol content of the sample, the greater the output current of the fuel cell. By precisely measuring the current produced in the fuel cell, an accurate measure of Breath alcohol content (BAC) is recorded.
As a warning to consumers, fuel cell technology accuracy and reliability is in stark contrast to the inexpensive and inaccurate semiconductor technology used in many cheap personal breathalyzers. Semiconductor technology is unreliable and imprecise and never to be trusted for accurate readings in a breathalyzer.
The relationship between blood alcohol content and breath alcohol content is well understood. Alcohol excreted in the breath is directly proportional to the alcohol in the blood stream. As blood alcohol concentration rises, peaks and falls during and after consuming alcohol so too does alcohol exhaled in the breath. This is the underlying principle for using breathalyzers to measure levels of intoxication. A quality fuel cell breathalyzer, when properly administered, provides a very accurate measure of alcohol intoxication.
There is a similar, but looser, relationship between blood alcohol content and transdermal alcohol content. TAC can also capture the rise, peak and fall of blood alcohol content but the TAC measurement has been found to be delayed by many minutes, even hours, from the actual alcohol concentration in the blood stream. Individual TAC results are not reliable equivents to blood alcohol content in the same way that breath measurements are.
Breathalyzer technology is ideal for roadside DUI checks because it provides an accurate and precise indication of blood alcohol content at the moment of the test. TAC technology, like SCRAM, is well suited to continuous monitoring for the presence of alcohol in the blood stream.
SCRAM is not available on the consumer market. It is reserved for court mandated alcohol offender monitoring. Professional Law Enforcement breathalyzers are priced out of the reach of most consumers. More affordable personal fuel cell breathalyzers are available to the public. Semiconductor breathalyzers should never be considered.