DUI Speedy Trials: The Margin of Error as a Key to Acquittal
In speedy DUI trials, conviction seems automatic. If the breathalyzer ticket reads over 0.60 mg/l in expired air, many public defenders recommend settling for the minimum penalty (fine and 8 months without a license) to obtain the one-third reduction. However, at Alonso Sala, we do not accept automatic plea bargains. In 2026, technical defense has achieved significant victories questioning the metrology of the devices and breaking the presumption of the machine's veracity.
The Battle of the Margin of Error (PEM)
No device is perfect. Every breathalyzer, no matter how advanced, has a Maximum Permissible Error (PEM). Order ITC/155/2020 regulates these margins, but the Prosecution systematically tends to ignore them or apply the "verification" margins (lower) instead of the "in-service" margins (higher).
The difference is vital. For an in-service breathalyzer, the error margin is 7.5% for rates above 0.40 mg/l (or 0.030 mg/l for low rates). Practical example: If you tested 0.64 mg/l, the Prosecution will charge you with a crime. But if we apply the 7.5% error margin, the proven real rate could be 0.59 mg/l. By dropping below 0.60 mg/l, the fact ceases to be a crime and becomes an administrative infraction (fine and points, but no criminal record or trial). Fighting for those decimals is fighting for your freedom.
Evidential Breathalyzer vs. Screening Device
The small device used at roadside checkpoints (screening or approach breathalyzer) is not the same as the large "suitcase" found in the van or police station (evidential breathalyzer). Only the ticket from the evidential one has full probative value. We have won cases where the conviction was based solely on the first preliminary test, achieving the total annulment of the sentence for violation of fundamental rights.
The Widmark Curve and the Ascending Rate
Alcohol does not affect everyone equally at all times. From the moment the last drink is consumed, the blood alcohol level rises for 60-90 minutes (ascending phase) and then falls. If an hour passed between driving and the test, it is possible that you were driving sober (initial absorption phase) and tested positive later (peak maximum). Through toxicological expert reports based on the Widmark formula, we can reconstruct the real rate at the moment of driving, which is the only relevant one for the crime.
Procedural Guarantees: Your Last Line of Defense
Many drivers are unaware of their right to request a contrast blood test at a nearby hospital. If the police did not adequately inform you of this possibility, or if they refused to transport you alleging lack of means, your right of defense has been violated. This defenselessness can lead to the radical nullity of the breath test, leaving the prosecution without evidence and forcing a free acquittal.