Portable Breath Alcohol Testers (PBTs) are an important tool used by Law Enforcement to increase roadside checkpoint effectiveness. Police use of portable fuel cell breath testers is known to result in higher and more accurate detection rates of impaired drivers than does officer judgment alone.
Contrary to what you might hear from an eager DUI attorney or from the many breathalyzer myths, law enforcement fuel cell alcohol testers such as the Lifeloc FC Series are highly precise and reliable instruments. The U.S. Department of Transportation (DOT) has strict accuracy requirements for professional testers. Each State that uses PBTs also have rigorous procedures for their maintenance and calibration. When properly calibrated and administered, a professional breath alcohol instrument will record a highly accurate measure of breath alcohol content (BAC). You may fool an officer with breath mints but you won’t fool a fuel cell breathalyzer.
States normally legislate that portable breath testers be permitted, but they are not required, to assist an officer in determining whether a suspected offender is DWI at roadside. Unless the instrument has been approved for "evidential" breath tests, the results cannot be used to establish the driver’s BAC in court. In most cases roadside breath testing is treated as a preliminary screening, and is followed up with additional "evidential" testing by blood or breath at the station or in a mobile police lab.
The PBT device does not replace standard roadside sobriety testing or mean that an officer does not have to follow standard arrest procedures. It is one of several tests that can be used to judge a subject's degree of intoxication.
Passive alcohol testing can detect the presence of alcohol in the exhaled breath near the driver’s mouth or sense the presence of alcohol in open drink containers. Passive testing, however, cannot provide quantitative measurement of BAC level, and if a device claims to do so, they are misrepresenting the science of alcohol breath testing. Passive testing does not require the subject to blow into a mouthpiece, and therefore does not obtain a precise or pure sample. Thus the breath sample is not measured into the device, and as well is not pure breath; it is mixed with ambient air. No accurate reading can be obtained from such a sample.
While passive test results cannot provide BAC level, they are an indicator as to whether further testing is required. Their value derives from the fact that for quick, preliminary screening, the testing can be conducted very quickly and non-invasively, without need for using a mouthpiece.
Passive testers are used where direct testing is either not practical or not required. For example, to assess whether an unconscious person who is unable to give a breath sample may have been drinking. They are also used in schools to help deter underage drinking, especially in zero tolerance situations.
Law Enforcement breath alcohol testers use either fuel cell or infrared technology to measure breath alcohol content. Fuel Cell testers are compact and highly accurate. Infrared systems are larger, more expensive and generally used at police stations to test DUI suspects. Both technologies are alcohol specific; that is they are not triggered by substances other than alcohol.
Semiconductor alcohol testing (Tin Oxide Sensor) is not used by Law Enforcement as the technology is not alcohol specific, lacks precision and lacks consistency.