A preliminary breath tester or portable breath test device (PBT) is a screening device used to obtain an indication of a DUI suspect’s breath-alcohol concentration at the scene of a car stop or DUI investigation. In a Mass. drunk driving case, PBT readings are admissible only on the issue of probable cause for arrest, and not on the issue of whether the person arrested was driving under the influence of alcohol.

Typically, the preliminary breath test is administered prior to arrest, as the last field sobriety test, to assist the officer in making the decision whether or not to arrest the driver. Because of their accuracy limitations, portable breath test results are, rightfully, not admissible in Massachusetts drunk driving trials. This is because G.L. c. 90 § 24K requires that BAC readings must be generated by a breathalyzer which uses infrared technology to be admissible to prove a DUI case.Numerous several scientific studies have resulted in findings that preliminary breath test devices such as the Alco-Senser are inherently inaccurate for use in drunk driving cases.

The preliminary or portable breath test devices used in Massachusetts use a fuel cell to determine alcohol content, instead of infrared spectrometry, which is more reliable. Chemicals such as acetaldehyde, methanol, isopropanol and propranolol can register as ethanol, the alcohol found in alcoholic beverages. Also, they are susceptible to registering false readings due to residual mouth alcohol. 

Good Massachusetts DUI lawyers routinely and automatically file motions in limmine to exclude Weston PBT breath test results. Due to their limitations, PBTs can only be used as part of a DUI preliminary screening process, because they do not have the same accuracy or reliability as evidential breathalyzers.

These PBT devices are used to test a motorist within minutes of an initial DUI traffic stop and they are not sufficiently accurate to establish anything more than probable cause for a DUI arrest. Therefore, their results are completely inadmissible to prove the prosecution’s case. Also, preliminary breath testing procedures not usually incorporate the same safeguards or documentation which is required for actual breathalyzer tests. Unlike breathalyzers, PBTs do not use simulator solution to perform a calibration standard analysis. Due to the inherent limitations of PBTs, their accuracy and reliability can easily be challenged. Also, in order to administer a PBT in a Massachusetts OUI case, the officer administering the test must be specifically certified to do so. A general breath test operator certificate is insufficient to qualify a police officer to use a PBT.

The PBT is not part of the implied consent law. This means that refusing to submit to a preliminary breath test or portable breath test will not result in a breathalyzer refusal suspension in Massachusetts. However, in some other states, refusing to submit to a preliminary breath test will have license suspension and other consequences. Some states treat refusal to submit to a PBT in a DUI case as a civil infraction.