Lawyers for Breathalyzer Challenge

The breathalyzer test is the cornerstone of prosecution evidence in DUI cases. However, these devices are subject to strict regulatory requirements regarding calibration, maintenance, and administration protocols. Any deviation from these requirements can render the test result inadmissible, leading to case dismissal.

Legal Framework: Grounds for Challenge

Our technical defense examines: calibration records (breathalyzers must be calibrated periodically by authorized laboratories; expired or missing calibration records invalidate results), administration protocol (mandatory 15-minute observation period to prevent false positives from residual mouth alcohol, regurgitation, or recent drink consumption), measurement margin of error (±7.5% for evidential breathalyzers), and chain of custody (proper documentation of the device used, officers involved, and environmental conditions).

Defense Strategies

When the breath test is the sole evidence, a successful challenge effectively eliminates the prosecution's case. We request production of the full device maintenance log, officer training certifications, and video recordings of the testing procedure. In borderline cases (readings close to the 0.60 mg/l criminal threshold), the margin of error alone may be sufficient to create reasonable doubt.

Margin of Error & Double Measurement

The evidential breathalyser carries a recognised metrological margin of error: ±5% for readings up to 0.40 mg/l and ±7.5% above that. Where the result is close to the 0.60 mg/l threshold —the line between an administrative infraction and the criminal offence of Art. 379.2 CP— correctly applying this margin can place the conduct below the criminal line. The two mandatory readings, taken at least 10 minutes apart, must also be consistent, and the defence insists on applying the more favourable of the two.

Criminal Consequences

If the challenge does not succeed and the result stands, the drink-driving offence of Art. 379.2 CP carries, in the alternative, prison of 3 to 6 months, a fine of 6 to 12 months or community service, together with the deprivation of the right to drive of 1 to 4 years. For a first offence the prison term is usually suspended, so the licence deprivation tends to be the most onerous consequence. This is precisely why neutralising the breath result —or reducing it below the 0.60 mg/l threshold through the margin of error— is so decisive: it is the difference between a conviction and an acquittal.

Metrological control of the breathalyser: the first line of challenge

The evidential-grade breathalyser that produces a result with probative value is not just any device: it is subject to State metrological control under Royal Decree 244/2016. That control covers the approval or model evaluation of the instrument and, above all, the periodic verification confirming that the specific device still measures within its tolerances. When we defend a charge under Article 379.2 of the Criminal Code, the first thing we demand from the police report is the documentation proving that the breathalyser used held a valid periodic verification, as well as verification after any repair.

The absence of that documentation, or an expired certificate, is no minor technicality. The reading is a technical expert measurement and its reliability rests on the instrument having been calibrated to standard. If the device cannot evidence its metrological control, the result loses the solidity the prosecution needs to sustain a conviction, and the way opens to argue whether the figure shown is truly the driver's level or merely an unguaranteed datum. Checking the device serial number recorded in the report and cross-referencing it against its verification history is a check we carry out systematically.

Double measurement, the regulatory interval and applying the error margins

A breath-alcohol test with incriminating value does not end with a single blow. The protocol requires a first measurement and a second after the regulatory interval has elapsed, precisely to rule out residual mouth alcohol and to confirm the consistency of the results. Where the report does not record that interval, or where the two figures diverge anomalously, there is material to question the technical validity of the test. Reviewing the exact time of each measurement noted by the officer is painstaking work that frequently reveals departures from the procedure.

To this we add the error margins that the metrological standard itself acknowledges in the instrument. Every measurement carries an associated uncertainty, and when the result sits very close to the criminal threshold of Article 379.2 (0.60 milligrams per litre of exhaled air, equivalent to 1.2 grams per litre in blood), deducting the error margin may place the real level below the boundary of the offence. In these near-threshold cases, the defence argues that the presumption of innocence requires taking the figure most favourable to the driver, which can move the conduct out of the criminal sphere and into the merely administrative one.

The right to contrast the result through a blood test

A driver subjected to the breath test is not at the mercy of the breathalyser figure: they have the right to contrast that result through a blood test, and the officer is obliged to inform them of that option. This right is an essential safeguard, because a blood analysis carried out at a health centre offers a direct determination of the alcohol level that can confirm or contradict the device's reading. Where the report does not evidence that this second contrasting test was offered, or where it was denied to the person, the defence invokes it as a shortfall that weakens the probative force of the result.

The frustration of this right is especially relevant in borderline cases, where the difference between the Article 379.2 offence and a simple administrative infraction can be a matter of hundredths. The challenge here is not aimed at denying that driving took place, but at disputing the lawfulness and reliability of the evidence under Article 11.1 of the Organic Law of the Judiciary, which excludes the effect of evidence obtained in breach of fundamental rights. Documenting what information the driver received and what alternatives were offered at the moment of the stop is decisive in building this line of defence.

Criminal versus administrative boundary, fast-track trial and prescription

Not every blood-alcohol reading is a crime. It is always worth distinguishing the criminal offence from the administrative infraction under the Traffic Law (Royal Legislative Decree 6/2015): below the threshold of Article 379.2 of the Criminal Code, the conduct is penalised administratively with a fine and points, not with criminal consequences. The same distinction applies to the saliva drug test, which is merely indicative and requires confirmatory laboratory analysis, and to driving under the influence of drugs (Article 383 and the influence modality of 379.2), where the mere presence of the substance is not enough: it must be shown that it affected the ability to drive.

These offences are typically tried through the fast-track procedure (Articles 795 onwards of the Criminal Procedure Act): the Investigating or Duty Court instructs and the Criminal Court tries the case, often with the possibility of a guilty-plea agreement. The penalty is not limited to imprisonment, a fine or community work: it also includes deprivation of the right to drive motor vehicles and mopeds under Article 47 of the Criminal Code, the consequence that most affects a driver's daily life. As for prescription, under Article 131 of the Criminal Code and given that these offences carry a maximum penalty of no more than five years, they prescribe after five years.