DUI Defense Strategies FAQ

Challenging the legality of the traffic stop is one of the most effective DUI defense strategies because if the stop was unlawful, all evidence obtained afterward (field sobriety tests, breathalyzer results, blood tests, officer observations) can be suppressed under the Fourth Amendment exclusionary rule. Under California law and the Fourth Amendment, a police officer must have reasonable suspicion of criminal activity or a traffic violation to justify a traffic stop. Reasonable suspicion requires specific, articulable facts that would lead a reasonable officer to suspect a traffic violation or criminal activity, not just a hunch or generalized suspicion.

Common grounds for challenging traffic stops include claiming the officer had no valid reason for the stop (no observed traffic violation or erratic driving), the alleged traffic violation didn't actually occur (dashcam video contradicts officer's claims), anonymous tips without corroboration (insufficient for reasonable suspicion under Navarette v. California), DUI checkpoints that don't comply with Ingersoll requirements (advance publicity, supervisor approval, neutral selection criteria), and pretextual stops where the officer stopped you for a minor violation as pretext to investigate DUI without reasonable suspicion. Your attorney can file a motion to suppress evidence under Penal Code Section 1538.5, arguing the stop violated your Fourth Amendment rights. If successful, the prosecution cannot use any evidence obtained after the illegal stop, which often results in case dismissal. Dashcam and bodycam video are critical evidence in these motions, as they provide objective evidence of your driving and the officer's stated reasons for the stop. Even seemingly minor inconsistencies between the officer's report and video footage can establish lack of reasonable suspicion and result in suppression.

The rising BAC defense, also called rising blood alcohol defense or absorption defense, argues that your blood alcohol concentration was below the legal limit of 0.08% while you were actually driving, but rose above the limit by the time you were tested 30 minutes to 2 hours later. This defense is based on the scientific fact that alcohol takes time to absorb into your bloodstream after consumption, typically 30 minutes to 2 hours to reach peak BAC levels. During this absorption phase, your BAC is continuously rising even after you stop drinking. If you consumed alcohol shortly before driving, your BAC may have been below 0.08% while driving but continued rising during the time between when you stopped driving and when you were tested.

The rising BAC defense is particularly effective when you consumed alcohol within 1-2 hours before driving, testing occurred 45 minutes or more after you stopped driving, your BAC was marginally above 0.08% (such as 0.09% to 0.11%), you have documented evidence of when and what you drank, and there's a significant time gap between driving and testing. To prove this defense, your attorney will typically hire a forensic toxicologist who can perform retrograde extrapolation calculations to estimate your BAC at the time of driving based on when you drank, what you drank, your body weight, gender, the time between drinking and testing, and your actual test result. The expert can testify that your BAC was below 0.08% while driving even though it tested above 0.08% later. This defense is especially powerful against VC 23152(b) per se charges because the prosecution must prove you were at or above 0.08% while driving, not while tested. It may still leave you vulnerable to VC 23152(a) impairment charges if other evidence shows you were impaired while driving. California jury instruction CALCRIM 2110 specifically allows this defense and requires jurors to consider whether your BAC was below 0.08% while driving even if it was above when tested.

Title 17 of the California Code of Regulations establishes strict procedures that law enforcement and medical personnel must follow when collecting, storing, and analyzing blood and breath samples for DUI prosecutions. These regulations ensure the accuracy and reliability of chemical test results. When law enforcement or crime labs violate Title 17 requirements, the chemical test results may be excluded from evidence or given less weight by the judge or jury. Title 17 violations are among the most technical but effective DUI defenses because they attack the scientific reliability of the prosecution's primary evidence of intoxication.

Common Title 17 violations include failure to observe the subject for 15 minutes before breath testing (to ensure no mouth alcohol, burping, or vomiting that could contaminate results), improper calibration or maintenance of breath testing devices (required every 10 days or 150 tests), blood samples not collected by qualified personnel (must be licensed medical professional or qualified technician), improper preservative or anticoagulant in blood vials (must contain sodium fluoride and potassium oxalate in proper amounts), blood samples not properly stored or refrigerated (can cause fermentation and falsely elevated BAC), broken chain of custody for blood samples, breath testing device not on the approved list maintained by the California Department of Public Health, failure to retain blood sample portions for independent defense testing, and laboratory analysis not performed according to proper procedures or by qualified criminalists. Your attorney can subpoena calibration records, maintenance logs, training certificates, lab protocols, and chain of custody documentation to identify Title 17 violations. Expert toxicologists can testify about how these violations affect result reliability. While Title 17 violations don't automatically result in evidence suppression, they can create reasonable doubt about BAC accuracy or result in reduced weight given to test results.

Yes, breathalyzer accuracy can be challenged through numerous defenses based on machine malfunctions, operator error, physiological factors, and Title 17 violations. Breathalyzers are sophisticated electronic devices that require proper calibration, maintenance, and operation to produce accurate results. Common challenges to breathalyzer accuracy include improper calibration or maintenance of the device (must be calibrated every 10 days or 150 tests under Title 17), failure to observe the subject for 15 minutes before testing (required to detect mouth alcohol), mouth alcohol contamination from recent drinking, burping, vomiting, or GERD, medical conditions like diabetes or acid reflux causing false positives, radio frequency interference from police radios or cell phones, improper administration by the officer (not following manufacturer protocols), and ambient air contamination in testing environment.

Specific breathalyzer models have known issues: the Draeger Alcotest 7110 has been shown to give falsely high readings when subjects have acid reflux, while older Intoxilyzer models are vulnerable to radio frequency interference. Your attorney can subpoena the specific device's calibration records, error logs, and maintenance history to identify malfunctions or missed calibrations. Expert witnesses can testify about the device's error rate, susceptibility to false positives, and impact of Title 17 violations on result reliability. Additionally, the breath test device's software source code is proprietary and not disclosed to defendants, creating a Confrontation Clause issue under Crawford v. Washington that some courts have recognized. Environmental factors like temperature (breath tests assume a core body temperature of 34°C, but fever or hypothermia changes this), breathing patterns (hyperventilating before the test can reduce BAC readings, while holding your breath increases them), and even dental work or dentures can trap alcohol and cause mouth alcohol issues. If you took the breath test at the roadside (preliminary alcohol screening or PAS test), these are even less reliable than evidentiary breath tests and can more easily be challenged. Many attorneys recommend subpoenaing the arresting officer to testify about their training, the device's maintenance, and the testing procedures to expose weaknesses in the breath test administration.

Blood test results, while generally more accurate than breath tests, are still vulnerable to numerous challenges based on collection procedures, storage conditions, contamination, and laboratory analysis. Under Title 17 of the California Code of Regulations and established forensic science protocols, blood samples must be collected, preserved, stored, and tested according to strict procedures. Violations of these procedures can render blood test results unreliable or inadmissible. Common defenses to blood tests include improper collection by unqualified personnel (must be licensed medical professional under Title 17 Section 1220.4), failure to use proper preservative and anticoagulant (must contain sodium fluoride and potassium oxalate), inadequate preservative or anticoagulant amounts (can cause coagulation or fermentation), and improper storage temperatures (must be refrigerated; room temperature storage causes fermentation and falsely elevated BAC).

Additional challenges include broken chain of custody (missing documentation of who handled the sample), contamination during collection (using alcohol swabs instead of non-alcohol antiseptic), hemolysis (breakdown of red blood cells affecting accuracy), fermentation (bacteria consuming sugar and producing alcohol in the sample), coagulation (clotted blood produces inaccurate results), failure to retain sample portion for independent defense testing (violates due process), and laboratory analysis errors or contamination. Your attorney has the right under California law to obtain a portion of the blood sample for independent testing by a defense expert. This can reveal preservative levels, fermentation, contamination, or improper storage. Expert toxicologists can testify about how these factors affect BAC results. In some cases, independent testing shows BAC significantly lower than the prosecution's results, creating reasonable doubt. Chain of custody challenges are particularly effective when the blood sample passed through multiple hands, sat in evidence storage for extended periods, or documentation is incomplete. The prosecution must establish an unbroken chain showing who handled the sample at each stage and that it was properly stored. Any gap in the chain creates doubt about whether the tested sample is actually your blood or whether it was contaminated or tampered with.

Field sobriety tests (FSTs) are notoriously unreliable and vulnerable to challenge based on improper administration, environmental factors, physical conditions, and officer subjectivity. The three standardized field sobriety tests approved by the National Highway Traffic Safety Administration (NHTSA) are the Horizontal Gaze Nystagmus (HGN), Walk-and-Turn (WAT), and One-Leg Stand (OLS). Even when administered perfectly under ideal conditions, these tests have significant error rates and can be failed by sober individuals. The tests are designed to be failed: they're administered on the roadside at night under stressful conditions while you're anxious, tired, and standing on uneven pavement in dress shoes or heels.

Common challenges to field sobriety tests include improper administration not following NHTSA protocols (officer deviated from standardized procedures), medical conditions affecting performance (inner ear problems, knee injuries, back problems, neurological conditions, obesity), age factors (people over 65 have difficulty with balance tests even when sober), environmental factors (uneven pavement, poor lighting, weather conditions, traffic noise), footwear issues (high heels, boots, sandals make balance tests nearly impossible), officer subjectivity (officers often see "clues" that don't exist), and fatigue or nervousness (creates same symptoms as impairment). For HGN testing specifically, many officers aren't properly trained in administering the test, can't distinguish nystagmus from normal eye movements, or fail to check for other causes of nystagmus (certain medications, neurological conditions, eye problems). For Walk-and-Turn, the test requires walking heel-to-toe on an imaginary line without using arms for balance, which many sober people fail. For One-Leg Stand, standing on one foot for 30 seconds while counting is difficult for anyone with balance issues, leg injuries, or who is overweight. Non-standardized tests like the finger-to-nose test, alphabet recitation, or counting backwards have no scientific validity and should be challenged as unreliable. Your attorney should obtain the officer's training records to determine if they're certified in SFST administration and whether they followed protocols. Dashcam or bodycam video is critical for challenging FSTs because it shows the actual conditions, your performance, and whether the officer followed proper procedures.

The mouth alcohol defense argues that residual alcohol in your mouth, rather than alcohol from your lungs (alveolar air), caused falsely elevated breath test results. Breathalyzers are designed to measure deep lung air that reflects blood alcohol concentration, but they cannot distinguish between alcohol from your lungs and alcohol from your mouth. When mouth alcohol is present, the breathalyzer produces artificially high BAC readings that don't accurately reflect your true blood alcohol level. This is why Title 17 requires officers to observe suspects for 15 continuous minutes before breath testing to ensure no burping, vomiting, drinking, eating, or smoking that could introduce mouth alcohol.

Common sources of mouth alcohol include recent drinking (within 20 minutes before the test), burping or belching (brings alcohol vapor from stomach to mouth), vomiting or regurgitation (coats mouth with alcohol), gastroesophageal reflux disease (GERD) or acid reflux (chronic condition causing stomach contents to enter esophagus and mouth), dental work or dentures (trap alcohol in crevices), breath mints or spray (often contain alcohol), chewing tobacco, and certain medications containing alcohol. If you have GERD or acid reflux, this is a particularly strong defense because these conditions cause chronic mouth alcohol that persists even with a 15-minute observation period. Medical documentation of GERD, prescriptions for reflux medication, or testimony about chronic heartburn can establish this defense. The failure to properly observe you for 15 minutes is a Title 17 violation that supports the mouth alcohol defense. Video evidence showing the officer didn't continuously observe you, or showing you burping or coughing during the observation period, can prove mouth alcohol contamination. Expert toxicologists can testify that even small amounts of mouth alcohol cause disproportionately high breathalyzer readings. Additionally, if you took two breath tests and the results differed significantly (more than 0.02% variance), this suggests mouth alcohol contamination on one of the tests, as true deep lung air samples should be very consistent.

Yes, numerous medical conditions can affect DUI field sobriety tests, breathalyzer results, and officer observations, potentially leading to false DUI arrests. These conditions can mimic signs of intoxication or interfere with chemical test accuracy, providing strong defenses when properly documented and presented. Common medical conditions affecting DUI cases include diabetes and hypoglycemia (low blood sugar causes confusion, disorientation, slurred speech, and unsteady gait identical to intoxication; ketoacidosis produces acetone on breath that breathalyzers can mistake for alcohol), acid reflux and GERD (causes mouth alcohol contamination of breath tests), neurological conditions (multiple sclerosis, Parkinson's, brain injury, stroke cause poor balance, slurred speech, and jerky eye movements misinterpreted as intoxication), respiratory conditions (asthma, COPD, emphysema affect ability to provide adequate breath sample), and inner ear problems (vertigo, Meniere's disease, ear infections cause balance problems affecting field sobriety tests).

Additional conditions include arthritis and joint problems (make it impossible to perform heel-to-toe walking or one-leg stand), obesity (affects balance and ability to perform physical tests), anxiety and panic attacks (cause hyperventilation, trembling, confusion under stress of traffic stop), thyroid disorders (hypothyroidism causes fatigue, slow speech, poor coordination), and auto-brewery syndrome (rare condition where gut bacteria ferment carbohydrates into alcohol). To use medical conditions as a defense, you should obtain medical records documenting the condition, prescriptions for related medications, doctor's testimony about how the condition affects sobriety test performance, and expert testimony explaining the condition to the jury. Video evidence showing your symptoms is also valuable for demonstrating that your appearance and behavior resulted from medical conditions rather than intoxication. Some medical conditions like diabetes can also cause falsely high breathalyzer results because ketones in the breath can be misread as alcohol by some breath testing devices. If you have any of these conditions, inform your attorney immediately and provide all medical documentation, as this can be the difference between conviction and acquittal or dismissal.

The partition ratio defense challenges the fundamental assumption used by breathalyzer devices to convert breath alcohol to blood alcohol concentration. Breathalyzers use a fixed partition ratio of 2100:1, meaning they assume that 2100 milliliters of alveolar (deep lung) air contains the same amount of alcohol as 1 milliliter of blood. However, this ratio varies significantly among individuals based on body temperature, breathing patterns, hematocrit levels (red blood cell concentration), and individual physiology. Studies show the actual partition ratio ranges from 1300:1 to 3000:1 in different people, with an average around 2100:1.

If your actual partition ratio is higher than 2100:1 (for example, 2500:1), the breathalyzer will overestimate your true BAC. Factors affecting partition ratio include elevated body temperature (fever or hot environment increases the ratio, causing falsely high BAC readings), hyperventilation (increases ratio), breath-holding before testing (decreases ratio), hematocrit levels (anemia increases partition ratio), recent exercise (increases body temperature and metabolism), and gender differences (women tend to have slightly different ratios than men). For someone with a partition ratio of 2500:1, a breath test reading of 0.10% might correspond to a true blood alcohol of only 0.084%, which is below the legal limit. Expert witnesses can testify about partition ratio variability and how it affects your specific case. This defense is particularly effective when your breath test was marginally above 0.08% (such as 0.09% to 0.10%), you had a fever or were in a hot environment, you exercised recently before the arrest, or you have documented medical conditions affecting your partition ratio. The partition ratio defense can create reasonable doubt about whether your true BAC was above the legal limit, especially when combined with other defenses like rising BAC or Title 17 violations. This is a technical defense requiring expert testimony, but it can be very persuasive with juries because it exposes the scientific limitations and assumptions built into breath testing technology.

Video evidence from police dashcams, bodycams, jail booking cameras, and private surveillance can provide powerful exculpatory evidence in DUI cases by contradicting officer testimony and showing you were not as impaired as claimed. Many DUI arrests involve significant exaggeration of impairment symptoms in police reports, and video evidence can expose these exaggerations. Your attorney should immediately request all video evidence through discovery motions and subpoenas. Common types of helpful video include dashcam footage showing normal driving before the stop (contradicts claims of weaving or erratic driving), bodycam footage showing your performance on field sobriety tests (often shows you performed better than officer's report claims), jail booking video showing you walking normally and speaking clearly (contradicts claims of severe intoxication), and private surveillance from businesses or homes near the arrest location.

Video evidence is particularly valuable for showing the officer failed to conduct the 15-minute observation period before breath testing (Title 17 violation), your field sobriety test performance was better than described in reports, environmental conditions made field sobriety tests unfair (uneven pavement, poor lighting, heavy traffic), the officer improperly administered field sobriety tests (didn't follow NHTSA protocols), you appeared sober and coordinated at booking (contradicts extreme intoxication claims), and the traffic stop was pretextual or lacked reasonable suspicion. In some cases, video shows you never actually drove the vehicle (passenger was driving, or you were sitting in parked car), which defeats the "driving" element required for DUI conviction. Officers know their actions are being recorded, but they often forget about jail booking cameras and dashcams from other nearby patrol vehicles. Your attorney should request video from all sources including neighboring patrol cars, jail booking, any private businesses with cameras in the area, and residential security cameras. Video evidence is objective and juries give it tremendous weight, often more than officer testimony. In many cases, video evidence showing you were not nearly as impaired as the police report claimed can lead to reduced charges (wet reckless instead of DUI) or complete dismissal of charges.