DUI Defense
Short answer: every Memphis DUI case turns on three questions. Was the stop lawful? Was the arrest supported by probable cause? Is the chemical or observational evidence admissible and reliable? The field sobriety tests, the breath instrument and the blood draw each have known failure points, a line of Tennessee and U.S. Supreme Court cases decides what can be suppressed, and a short list of facts about the stop, the driver and the testing conditions changes outcomes more than anything else.
This page is the detail behind our Memphis DUI lawyer page, on how the case is actually fought. Call (901) 324-5000, or call or text the criminal line at 901-412-2973, any time. Se habla español.
Field Sobriety Tests and Breathalyzers — What the Science Actually Shows
Standardized Field Sobriety Tests (SFSTs)
The three tests validated by the National Highway Traffic Safety Administration (NHTSA) are the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn, and the One-Leg Stand. Officers and prosecutors present these as objective measures of impairment. They are not.
- NHTSA’s own validation studies pegged combined accuracy at roughly 91% — but only when administered on a dry, level, well-lit surface to a subject with no medical conditions, no footwear issues, no inner-ear problems, and not more than 50 pounds overweight. Roadside conditions rarely match.
- HGN can be influenced by caffeine, nicotine, prescription medications, head trauma, certain neurological conditions, and even the flashing lights on the patrol car behind you.
- Walk-and-Turn and One-Leg Stand are designed so the average sober person is expected to make at least one “clue” the officer is trained to score against you. A single clue on the Walk-and-Turn is not a fail; two clues out of eight possible scoring categories can be enough for the officer to report failure.
These tests are voluntary in Tennessee. You cannot be punished for declining them — unlike chemical tests, which trigger implied-consent revocation if refused.
Breath Testing
Tennessee uses the Intoximeter EC/IR II as its evidential breath testing instrument. The device does not measure alcohol directly — it infers blood alcohol by measuring alcohol in expired breath and applying a population-average ratio of 2,100:1. Your actual blood-to-breath ratio may be significantly different, which can skew results up or down.
Common issues that a defense attorney will examine:
- 20-minute observation period. The officer is required to observe you continuously for at least 20 minutes before the test — no belching, burping, regurgitation, or putting anything in your mouth. Failure to document this period can compromise the result.
- Instrument certification and calibration records under the Tennessee Bureau of Investigation’s protocols.
- Mouth alcohol from dental work, recent alcohol consumption, GERD, or acid reflux can produce artificially elevated readings.
- Interfering substances — certain industrial exposures, ketones (in diabetics or low-carb dieters), and some inhalers can trigger false positives.
- Rising blood alcohol curve. If you drank shortly before driving, your BAC at the time of the test may be significantly higher than at the time you were behind the wheel — a defense worth investigating when the arrest-to-test interval is long.
Blood Testing
Blood tests are presumed more accurate than breath but are not beyond challenge. Chain of custody, storage conditions, the sterilant used on the draw site (alcohol-based swabs should never be used), gas chromatography calibration, and analyst qualifications are all proper subjects for cross-examination and motions to suppress.
Key Tennessee Case Law Every DUI Defendant Should Know
The DUI statutes are only half the story. Tennessee’s appellate courts and the United States Supreme Court have shaped what the State must prove, what officers can do at the roadside, and when chemical evidence is admissible. The cases below are the ones most often litigated in motions practice in Shelby County DUI cases.
State v. Lawrence, 849 S.W.2d 761 (Tenn. 1993) — “Physical Control” and the Totality of the Circumstances
Lawrence is the foundational Tennessee case on what it means to be in “physical control” of a vehicle under T.C.A. § 55-10-401. The defendant was found asleep behind the wheel of his truck, parked in a roadway, engine off, keys in his pocket. The Tennessee Supreme Court rejected a rigid three-part test and adopted a totality-of-the-circumstances approach. Factors include the location of the vehicle, the position of the driver, the location of the keys, whether the engine is running, the time of day, and whether the vehicle is operable. The lesson for defendants: there is no bright-line rule. A skilled defense identifies the Lawrence factors that cut in your favor — vehicle off the roadway, keys away from the ignition, evidence the defendant was sleeping it off rather than preparing to drive.
State v. Reynolds, 504 S.W.3d 283 (Tenn. 2016) — Warrantless Blood Draws and the Good-Faith Exception
After a fatal single-vehicle accident, deputies directed hospital staff to draw blood from the injured defendant without a warrant and without actual consent. The Tennessee Supreme Court held that the warrantless blood draw violated both the Fourth Amendment and Article I, § 7 of the Tennessee Constitution — but it adopted, for the first time in Tennessee, the good-faith exception to the exclusionary rule. The result is a fact-intensive inquiry: officers who relied in objectively reasonable good faith on then-binding precedent may avoid suppression; officers who departed from procedure or moved after the law had clearly shifted may not. Reynolds governs nearly every motion to suppress a warrantless blood test in Tennessee today.
Missouri v. McNeely, 569 U.S. 141 (2013) — Natural Dissipation of Alcohol Is Not a Per Se Exigency
Before McNeely, some prosecutors argued that the body’s metabolism of alcohol itself created exigent circumstances justifying any warrantless blood draw. The U.S. Supreme Court rejected that categorical rule. Exigency must be evaluated case-by-case under the totality of the circumstances. After McNeely, the State cannot rely on the passage of time alone — it must point to specific facts (a serious crash demanding immediate medical attention, distance from a magistrate, etc.) that prevented obtaining a warrant.
Birchfield v. North Dakota, 136 S. Ct. 2160 (2016) — Breath vs. Blood
Birchfield drew a constitutional line between breath and blood. A breath test is permissible as a search incident to a lawful DUI arrest without a warrant; a blood test, because it pierces the skin and yields a sample retainable by the State, is not. The decision also held that states cannot criminalize the refusal of a blood test absent a warrant — though they may impose civil consequences such as license revocation. This is why Tennessee’s implied-consent refusal is treated as a civil violation rather than a separate crime.
Mitchell v. Wisconsin, 139 S. Ct. 2525 (2019) — The Unconscious-Driver Rule
When a DUI suspect is unconscious and cannot be given a breath test, the exigent-circumstances doctrine almost always allows a warrantless blood draw, because the officer must also tend to the medical emergency. Mitchell is most often invoked in serious-injury and fatality cases where the driver is brought to a hospital before any chemical testing has occurred.
Rodriguez v. United States, 575 U.S. 348 (2015) — Prolonged Stops
A traffic stop may not be extended — even briefly — beyond the time reasonably required to address the traffic infraction unless the officer develops independent reasonable suspicion. In a DUI case, that often means scrutinizing the timeline: how long did the officer chat about the citation before pivoting to questions about drinking? Was a K-9 unit called after the stop should have ended? Rodriguez questions can produce suppression of every observation that follows the unlawful extension.
Michigan Dep’t of State Police v. Sitz, 496 U.S. 444 (1990), and State v. Downey, 945 S.W.2d 102 (Tenn. 1997) — Sobriety Checkpoints
Properly operated sobriety checkpoints are constitutional. But Tennessee’s appellate courts will scrutinize whether the checkpoint was supervised, whether neutral criteria governed which vehicles were stopped, and whether officers exceeded the scope of a brief screening encounter. A poorly run checkpoint is a defensible checkpoint.
Circumstances That Can Materially Affect the Outcome
No two DUI cases are alike. The same statutory charge can produce very different results depending on facts the client may not realize are important. The categories below tend to move the needle most often in Shelby County and West Tennessee DUI litigation.
Facts About the Stop Itself
Was the stop based on an articulable moving violation or a hunch dressed up as one? Did the officer observe weaving for several seconds across multiple lane lines, or a single momentary touch of the centerline? Was the stop based on an anonymous tip that was never independently corroborated? Was the officer outside of his or her jurisdiction? Was the stop unduly prolonged in violation of Rodriguez? Each of these can support a motion to suppress under the Fourth Amendment and Article I, § 7.
Whether the Driver Was Actually Driving
Lawrence “physical control” cases turn on where the keys were, whether the engine was warm, whether the headlights were on, where the car was located, and whether circumstantial evidence shows the defendant drove to the location while intoxicated. A client who pulled over to sleep it off, a passenger who slid behind the wheel to listen to the radio, a car parked in a private driveway — these are very different cases on the same statute.
Medical Conditions and Prescription Medications
Diabetes, GERD, acid reflux, certain neurological and inner-ear conditions, and recent head trauma can all produce signs that mimic intoxication or skew chemical testing. A diabetic in ketosis can register elevated readings on certain breath instruments. Prescription medication taken as prescribed does not categorically defeat a DUI charge, but it can change the theory of the case — and it can support a motion to introduce medical evidence at trial.
Officer Training and Certification
Was the officer certified to administer the SFSTs at the time of the arrest? Did the breath operator have a current operator permit? Were the calibration and maintenance records of the Intoximeter complete and contemporaneous? A lapsed certification or a gap in calibration logs can render evidence inadmissible.
Video Evidence
Dash-cam, body-cam, and station-house booking video often contradicts the officer’s written narrative. A defendant who is described in the report as “swaying” and “slurred” may appear calm and articulate on video. Conversely, video can hurt — which is why early review by counsel matters before plea decisions are made.
BAC Just Above the Limit
A reading of 0.08 or 0.09 is meaningfully different from a 0.18. Breath instruments have a published margin of error, often cited at +/- 0.005 to 0.01. Combined with the rising-curve defense in cases where drinking was recent, a “just over” reading is often the most defensible BAC case at trial.
Conditions of the Roadside Tests
NHTSA’s validation studies assume a dry, level, well-lit surface. Gravel shoulders, rain, sleet, a sloped berm, traffic noise, the rotating lights of the patrol car, and the officer’s flashlight in the eyes all degrade the reliability of the tests. Footwear matters: high heels, dress shoes, work boots, and orthotics all interfere with the heel-to-toe walk.
Refusal vs. Confusion
A driver who asks for a lawyer, who asks the officer to repeat the implied-consent warning, or who attempts to provide a sample but cannot deliver enough breath volume due to a medical condition is not necessarily refusing. Tennessee courts distinguish a genuine refusal from confusion or inability, and the difference can preserve your license.
Personal Mitigation
For cases that resolve by negotiation rather than trial, mitigation matters: employment history, family responsibilities, military service, lack of prior record, voluntary entry into treatment, a clean record on bond, and willingness to install an interlock before the law requires it. Prosecutors and judges have discretion within statutory ranges, and a well-presented mitigation package can be the difference between a minimum sentence and an enhanced one.
Immigration and Professional-License Consequences
For non-citizens, even a misdemeanor DUI can affect immigration status, particularly when paired with other charges or a felony enhancement. For nurses, CDL holders, lawyers, real estate agents, teachers, and others with a state-issued license, a DUI conviction often triggers separate licensing-board review. These collateral consequences should be evaluated at the front end of the case, not after the plea is entered.
Talk to a Memphis DUI lawyer
Patrick Brooks handles every DUI case personally in Shelby County General Sessions, the Germantown, Bartlett and Collierville municipal courts, and Tipton and Fayette County. A first-offense DUI starts at $3,500, flat; the schedule is on what a DUI lawyer costs in Memphis. Call (901) 324-5000, or call or text the criminal line at 901-412-2973, any time. Se habla español.
Frequently asked questions
Can a DUI be dismissed if the stop was bad?
Yes. If the officer had no articulable reason for the stop, or prolonged it beyond its purpose, everything that followed, the field tests, the breath or blood result and the statements, can be suppressed, and a case without that evidence is usually dismissed or reduced.
Are field sobriety tests reliable?
Only under the conditions they were validated for, a dry, level, well-lit surface, a healthy subject and an officer following the NHTSA protocol exactly. Change any of those and the tests prove far less than the affidavit claims.
Can a breath test result be challenged?
Yes. The 20-minute observation period, the instrument’s certification and calibration records, and medical conditions such as reflux or diabetes all bear on whether the number means what the State says it means. Blood draws raise their own chain-of-custody and warrant questions.