Challenging the Alcotest Breath Test in New Jersey

Can an Alcotest Reading Be Challenged?

Yes. In New Jersey, the Alcotest is generally accepted as scientifically reliable — but a reading is only admissible in court if the state proves the machine was properly calibrated and certified, the operator was properly trained and certified, and the test was administered according to strict procedures. If any of those foundations is missing or defective, the reading can be challenged and, in some cases, kept out of evidence entirely. A number on a printout is not automatically proof of guilt.

What Is the Alcotest?

The Alcotest is the breath-testing instrument New Jersey police use at the station after a DWI arrest to measure a driver's blood alcohol concentration (BAC). Its reading is what the state relies on to prove a per se violation of N.J.S.A. 39:4-50 — driving with a BAC of 0.08% or higher — without having to prove observable impairment. Because that single number can decide a case, New Jersey courts hold the state to demanding standards before allowing it in.

The device takes two separate breath samples and uses two independent measurement methods (infrared and electrochemical) that must agree within a set tolerance. If the samples don't fall within acceptable ranges, the test is invalid and must be repeated.

The 20-Minute Observation Period

Before a valid sample can be taken, the operator must continuously observe the driver for at least 20 minutes. The purpose is to rule out mouth alcohol — alcohol lingering in the mouth from belching, regurgitation, vomiting, dental work, chewing gum, food, drink, or smoking — which can dramatically inflate a reading that is supposed to reflect deep-lung (alveolar) air.

If the officer stepped away, was completing paperwork, or otherwise failed to genuinely observe the driver for the full period, the reliability of the reading is open to question. This is one of the most common and practical issues examined in a breath-test case.

Foundational Records the State Must Produce

New Jersey's leading case on the Alcotest, State v. Chun, set out foundational requirements the state must satisfy for a reading to be admissible. Among the core documents typically required are:

• The most recent calibration record for the specific device used, showing it was checked and adjusted on schedule.
• The calibrating unit's certificates and the certification of the solutions and simulators used to calibrate it.
• Proof the operator held a valid Alcotest certification at the time of the test.
• The Alcohol Influence Report and downloaded data from the device for the test in question.

If those records are missing, incomplete, or defective, the reading may be excluded. New Jersey has seen this play out on a large scale: in litigation over one state coordinator's calibration practices, a large number of Alcotest results were called into question — a reminder that the paperwork behind the number matters just as much as the number itself.

Other Reasons a Breath Reading May Be Unreliable

Beyond the paperwork, several real-world factors can affect an Alcotest result:

• Medical conditions — acid reflux (GERD), diabetes, and certain other conditions can introduce mouth alcohol or affect the sample. A more severe version of this issue — a condition that prevents giving an adequate sample at all — raises a different question from an unreliable reading; see our page on medical inability to complete a breath test in New Jersey.
• Operator error — failing to follow the required sequence, an improper observation period, or ignoring an "ambient fail" or other error message.
• Machine issues — a device that was out of calibration, overdue for certification, or throwing errors.
• Rising BAC / absorption — the reading reflects the time of the test, which may differ from the BAC at the time of driving. New Jersey law limits how far this argument goes for a standard BAC charge — see our page on the rising blood alcohol defense in a New Jersey DWI case for why, and where it can still matter.

The breath test is only one part of a DWI case. Many stops also involve field sobriety tests, and refusing to provide a breath sample is a separate charge with its own consequences — see our breath test refusal guide. If the stationhouse room was recorded, that footage can also help confirm whether the observation period was genuinely continuous — see our page on dashcam and police video evidence in DWI cases. And a low or borderline reading doesn't automatically mean no case at all — New Jersey's DWI law also allows a conviction based on observed impairment alone; see our page on getting a DWI with a BAC under 0.08% in New Jersey.

Why This Matters for Your Case

Because the Alcotest reading drives so much of a DWI prosecution, scrutinizing how it was produced is often central to the defense. Even where the number is high, problems with calibration records, certification, the observation period, or the operator's procedure can change how — or whether — the reading is used, which in turn affects the penalties on the table and the overall approach to a first offense. The important thing is to have the evidence examined carefully rather than assuming the printout settles everything.