Massachusetts Breath Test and BAC FAQs: The Machine, the Rules, and Your Rights

The Alcotest 9510 measures the same breath sample two ways: infrared light absorption, since ethanol absorbs light at particular wavelengths, and an electrochemical fuel cell that oxidizes alcohol and produces a current proportional to its concentration. The two readings must tightly agree or the test aborts, and the infrared reading is the one reported. The firm’s page on breath test and blood alcohol science explains the machine in depth.

Under 501 CMR 2.14, a valid sequence is one adequate breath sample, a control standard analysis of known alcohol concentration, and a second adequate breath sample. The two samples must agree within plus or minus 0.02 blood alcohol content units, and if they do not, a new sequence must begin. Disagreement between samples is a sign the measurement, not the driver, is the problem.

Under 501 CMR 2.13, the breath test operator must observe the arrestee for no less than 15 minutes immediately before the test to ensure nothing enters the mouth. If anything does, the period must restart, and if the device reports mouth alcohol, the sequence ends and the observation begins again. Whether a real, uninterrupted 15-minute observation happened is a standard subject of cross-examination.

The test assumes the sample reflects deep lung air, which tracks blood alcohol. Alcohol lingering in the mouth from a recent drink or a regurgitation inflates the reading, which is why the regulations impose the observation period and why the device is designed to abort when it reports mouth alcohol.

Alcohol is absorbed from the stomach and intestines into the blood over time, so a driver’s level can be higher at the station than it was while driving. The station test measures one point on a moving curve. The science and its use at trial are explained on the firm’s breath test science page.

Generally no. Under Commonwealth v. Colturi, 448 Mass. 809 (2007), a breath test taken within a reasonable time of operation is admissible without expert retrograde extrapolation testimony, and the delay goes to the weight of the evidence. The longer the gap, the weaker the inference that the station number matches the driving number, and juries understand that argument.

Consolidated litigation in which a District Court judge found that the Office of Alcohol Testing had no written calibration protocols for the Alcotest 9510 until September 15, 2014, and later that OAT had withheld failed calibration worksheets from the defense. It ended with notice to roughly 27,000 defendants and a court-supervised exclusion of results that ran until April 18, 2019. The firm’s post on the exclusion era tells the full story.

If your case included an Alcotest 9510 breath test administered between June 1, 2011 and April 18, 2019, then under Commonwealth v. Hallinan, 491 Mass. 730 (2023), you are entitled to a conclusive presumption of egregious government misconduct in a motion to withdraw a guilty plea or for a new trial. You must still show the test influenced your decision to plead. An old conviction that still raises penalties today is worth a review.

For OUI purposes, no. Under G.L. c. 90, § 24 (1) (e), blood drawn by or at the direction of police is admissible in an OUI prosecution only with the defendant’s consent, and a search warrant does not substitute for consent. Commonwealth v. Bohigian, 486 Mass. 209 (2020).

Not without your consent, if the government did the testing: in Commonwealth v. Moreau, 490 Mass. 387 (2022), the State crime laboratory’s analysis of hospital-drawn blood without consent was suppressed. But under Commonwealth v. Gannett, SJC-13659 (2025), if the hospital itself tested your blood during treatment, a State analyst may convert the serum result in your medical records into a blood alcohol percentage, and that converted number is admissible.

Hospitals usually test serum or plasma rather than whole blood and report the result in milligrams per deciliter. Serum values run higher than whole blood values, so a conversion is performed before the number is expressed as a blood alcohol percentage. How that conversion was done is one of the first things reviewed in a blood case, as the science page explains.

No. Refusal evidence is inadmissible at trial under art. 12 of the Massachusetts Declaration of Rights. Commonwealth v. McGrail, 419 Mass. 774 (1995). The refusal instead carries Registry of Motor Vehicles suspension consequences, set out on the firm’s license suspension guide.

The device’s calibration and certification records from the Office of Alcohol Testing, the operator’s certification, the printed test sequence showing the control standard result and the two-sample agreement, and the booking video that shows whether the observation period actually happened. The breathalyzer defense page covers how each record is used.

Yes. Under Commonwealth v. Camblin, 471 Mass. 639 (2015), compliance with the statutes and regulations does not immunize a breath test device from a scientific reliability challenge, and a defendant may seek a Daubert–Lanigan hearing on the technology, as the Camblin defendant did.

Yes, in full. A test that follows a sobriety checkpoint arrest must satisfy the same regulations and is open to the same challenges, and a checkpoint case adds its own layer, because the stop itself must comply with the checkpoint guidelines. The firm’s pages on Massachusetts sobriety checkpoints and its DUI checkpoint FAQs cover that layer.

No number decides a case by itself. The result must survive the regulations, the observation period, the timing problem, and the machine’s own records, and juries acquit drivers with readings over 0.08 when the number does not hold up. The firm’s post on why a breathalyzer result does not establish guilt makes the argument, and a consultation is confidential: 617.936.0201.