In New Hampshire, you can politely refuse roadside field sobriety tests. They are voluntary, and declining them does not trigger the administrative license suspension that applies when you refuse a chemical test after arrest. That distinction matters enormously in practice, and most drivers do not know it at the moment an officer asks them to step out of the car.

Three things to understand right away:

• FSTs are voluntary under New Hampshire law. RSA 265-A:4 governs implied consent for chemical testing after arrest—not roadside physical tests. Refusing an FST carries no automatic license penalty.
• The National Highway Traffic Safety Administration (NHTSA) sets the protocols for the three Standardized Field Sobriety Tests (SFSTs) used by officers across New Hampshire. Those protocols matter because any deviation from them weakens the evidentiary value of the results.
• If you were arrested or are facing a DWI charge, contact Lydon Law promptly. Evidence like body-camera footage can be deleted quickly, and early action protects your ability to challenge what happened at the roadside.

Table of Contents

• What field sobriety tests in NH are and why officers use them
• The three NHTSA standardized tests: what each one measures
• Standardized versus non-standardized tests, and the errors that weaken results
• Are FSTs mandatory in New Hampshire?
• How reliable are FSTs, and what can cause a false result?
• How New Hampshire defense attorneys challenge FST evidence
• If you were arrested after a poor FST performance: what happens next
• Practical do’s and don’ts at the roadside
• Concrete steps to challenge FST evidence before and at trial
• Key Takeaways
• What the FST process looks like from the defense side
• Lydon Law’s approach to DWI and FST defense in New Hampshire
• Useful sources
• FAQ

What field sobriety tests in NH are and why officers use them

Field sobriety tests are roadside physical and divided-attention tasks that officers use during a pre-arrest stop to decide whether probable cause exists to arrest you for DWI. They are observational screening tools, not proof of guilt. An officer who suspects impairment will typically ask you to perform one or more of these tasks while watching for specific behavioral and physical signs.

Those signs include slurred speech, an odor of alcohol, bloodshot eyes, poor balance, and difficulty following multi-step instructions. Each observation feeds into the officer’s probable-cause determination. Critically, FST results alone do not establish guilt beyond a reasonable doubt at trial. They are one piece of a larger picture, and they are far more vulnerable to challenge than many people assume.

The practical contrast between FSTs and chemical tests is worth understanding clearly. FSTs are observational and voluntary: you can decline them without any automatic legal penalty. Chemical tests (breath, blood, or urine) are a different matter entirely. Under New Hampshire’s implied-consent statute, once you are lawfully arrested for DWI, you are deemed to have consented to chemical testing. Refusing a chemical test after arrest triggers administrative consequences, including license suspension, under RSA 265-A:30. That is a separate legal regime from the roadside FST, and confusing the two is one of the most common and costly mistakes drivers make.

Some agencies also use a Preliminary Breath Test (PBT) during pre-arrest screening, depending on local policy. A PBT is a handheld device distinct from the evidentiary breath test administered after arrest. NHTSA training materials note that chemical testing after arrest is governed by state law, while roadside screening practices vary by agency.

The three NHTSA standardized tests: what each one measures

NHTSA’s SFST curriculum identifies three standardized field sobriety tests: Horizontal Gaze Nystagmus (HGN), Walk-and-Turn (WAT), and One-Leg Stand (OLS). Each is designed to be administered and scored in a specific, scripted way so that results carry evidentiary weight. Here is what each test actually measures and where each one is weakest.

Horizontal Gaze Nystagmus (HGN)

HGN measures involuntary jerking of the eye as it tracks a moving stimulus, typically a pen or small flashlight. Officers look for three clues in each eye: lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus before 45 degrees. Six total clues are possible. NHTSA training treats a higher number of clues as an indicator of impairment.

The weakness here is significant. Nystagmus can be caused by conditions that have nothing to do with alcohol: inner-ear disorders, certain prescription medications, neurological conditions, and even caffeine or fatigue. Officers must also hold the stimulus at a precise distance and move it at a precise speed. Deviations from that protocol change the clue count and undermine the result. An ophthalmologist can be a powerful expert witness when HGN evidence is central to a case.

Walk-and-Turn (WAT)

WAT is a divided-attention test. The officer instructs you to take nine heel-to-toe steps along a real or imaginary line, turn in a specific manner, and return nine steps. Officers score multiple possible clues including starting too soon, stopping while walking, failing to touch heel to toe, stepping off the line, using arms for balance, making an improper turn, taking the wrong number of steps, and losing balance during instructions.

Surface conditions directly affect this test. Uneven pavement, a sloped shoulder, gravel, or poor lighting all create balance challenges that have nothing to do with alcohol. Footwear matters too: heels over two inches are supposed to be flagged by the officer, but that step is frequently skipped.

One-Leg Stand (OLS)

OLS requires you to stand on one foot, hold the other foot approximately six inches off the ground, and count aloud until told to stop. Officers look for several clues such as swaying, using arms for balance, hopping, and putting the foot down; a certain number of these indicate impairment under NHTSA criteria.

Age, weight, back or leg injuries, and inner-ear problems all affect balance independent of alcohol. The test is also physically demanding for anyone over 65 or with a body weight that affects equilibrium. Officers are trained to note these factors, but in practice that documentation is often missing from the report.

How the three tests compare

Test	What it measures	Primary confounders	Key evidentiary weakness
HGN	Physiological eye response	Neurological conditions, medications, inner-ear disorders	Requires precise stimulus speed and distance; hard to verify without video
Walk-and-Turn	Divided attention and balance	Surface, footwear, fatigue, age, injury	Environmental conditions rarely documented fully
One-Leg Stand	Balance and counting	Age, weight, injury, vestibular disorders	Short duration makes clue counts easy to dispute without video

Pro Tip: If you are ever in a position to observe or recall the roadside scene, note the exact surface (gravel, sloped asphalt, painted line), lighting conditions, and what footwear you were wearing. Officers are trained to record these details under NHTSA protocols, but they often do not. Your recollection can fill that gap for your attorney.

Standardized versus non-standardized tests, and the errors that weaken results

“Standardized” has a specific legal meaning in this context. An NHTSA-standardized test comes with scripted instructions the officer must read verbatim, a defined set of clues scored in a specific way, and training requirements under NHTSA and IACP curricula. That structure is what gives the test its validated evidentiary weight. When an officer skips a step, paraphrases the instructions, or scores a clue that was not observed under proper conditions, the standardization breaks down.

Non-standardized tests are a different category entirely. These include officer-devised tasks (reciting the alphabet from a middle letter, touching finger to nose, counting backward from a specific number), sobriety-related questions, or early-exit screening questions. None of these have been validated through NHTSA research, and their probative value in court is correspondingly weaker. A skilled defense attorney will highlight the difference between what NHTSA has validated and what an officer improvised at the roadside.

Common administration errors that defense counsel look for include:

• Giving instructions that differ from the scripted NHTSA language
• Failing to demonstrate the test before asking the subject to perform it
• Positioning the subject on an uneven or sloped surface when a flat one was available
• Observing from an angle that makes clue detection unreliable
• Failing to ask about or document medical conditions, injuries, or prescription medications
• Not recording the time, exact location, or surface description in the report
• Administering tests in poor lighting or adverse weather without noting those conditions

Pro Tip: Officers are required to note environmental conditions and subject-related factors in their reports. When those entries are missing, that absence itself becomes a defense argument. Ask your attorney to compare the officer’s report against the NHTSA checklist for what should have been documented.

Are FSTs mandatory in New Hampshire?

No. Field sobriety tests are not mandatory in New Hampshire, and refusing them does not trigger the administrative license suspension tied to chemical-test refusals under RSA 265-A:4. Officers are not required to tell you that FSTs are voluntary, which means many drivers perform them without realizing they had a choice.

The implied-consent law works differently. Under RSA 265-A:4 and the administrative suspension provisions of RSA 265-A:30, once you are lawfully arrested for DWI, you are deemed to have consented to a breath, blood, or urine test. Refusing that post-arrest chemical test carries automatic administrative consequences, including license suspension. That is the implied-consent regime. Roadside FSTs are outside it entirely.

For a deeper look at how chemical test refusals work in New Hampshire, the Lydon Law guide on whether to take a breathalyzer in NH walks through the specific consequences and considerations.

Here is a short, calm script you can use at the roadside if asked to perform FSTs:

• “Officer, I respectfully decline to perform field sobriety tests.”
• If asked why: “I am exercising my right to decline. I am not being uncooperative.”
• If arrested: “I am invoking my right to an attorney before answering any questions or submitting to any testing.”

Additional steps to take at the scene:

• Ask for the officer’s name and badge number.
• Note the time, location, and road conditions as soon as you can.
• Ask whether there is body-camera or dash-camera footage being recorded.
• Do not volunteer information about where you were, what you drank, or how you feel.

You can find the full text of New Hampshire’s implied-consent statute at the NH General Court’s RSA Chapter 265-A page.

How reliable are FSTs, and what can cause a false result?

NHTSA’s own training materials acknowledge that SFSTs were validated under controlled, ideal conditions. Real roadside stops are rarely ideal. Surface irregularities, poor lighting, weather, and a subject’s physical condition all affect performance in ways that have nothing to do with alcohol consumption.

The validation studies behind the SFSTs established that the tests can indicate impairment when administered correctly under good conditions. They do not establish that every poor performance means the driver was impaired. Sensitivity and specificity matter here: a test can be a useful screening tool while still producing false positives at a meaningful rate, particularly when conditions deviate from the validation environment.

Common non-alcoholic causes of poor FST performance include:

• Medical conditions: Vestibular disorders, inner-ear problems, neurological conditions, and prior head injuries all affect balance and eye movement.
• Age: Balance and coordination naturally decline with age, affecting OLS and WAT performance independent of alcohol.
• Injury: A bad knee, ankle, or back injury makes heel-to-toe walking and one-leg standing genuinely difficult.
• Footwear: High heels, boots, or worn soles affect balance on any surface.
• Surface and environment: Sloped pavement, gravel, wet roads, or poor lighting create conditions the NHTSA validation studies did not replicate.
• Fatigue: Exhaustion mimics impairment in balance and divided-attention tasks.
• Prescription medications: Many common medications affect eye movement, balance, or cognitive processing.
• Language and cognitive differences: Multi-step instructions delivered quickly can be difficult to follow for someone whose first language is not English or who has a cognitive processing difference.

The NHTSA SFST Participant Manual explicitly lists environmental and subject-related variables that officers should record because they can influence performance. When those records are absent, the reliability of the test result is genuinely in question.

How New Hampshire defense attorneys challenge FST evidence

The one-sentence answer: defense challenges focus on protocol errors, environmental confounders, gaps in officer training, and missing or inconclusive documentation. A well-prepared attorney does not simply argue that the test was unfair. They build a specific, documented record showing exactly where the administration deviated from NHTSA standards and why that deviation matters.

Here is the checklist of records experienced NH defense counsel demand in discovery:

1. Officer SFST certification records — initial training date, certifying agency, and any refresher training. NHTSA materials require periodic refresher training; a lapse in recertification weakens the officer’s qualifications to administer the tests.
2. Body-camera and dash-camera footage — the most important single piece of evidence. Video often contradicts the written report on clue counts, instructions given, and surface conditions.
3. Patrol notes and incident report — compare these against NHTSA’s documentation checklist to identify omissions.
4. PBT device records — calibration logs and maintenance records for any preliminary breath test device used at the scene.
5. Evidentiary breath machine records — calibration logs, operator certification, and maintenance history for the device used post-arrest.
6. Medical and hospital records — if the driver was injured or sought medical attention after the stop, those records may document conditions that explain poor FST performance.
7. Incident timeline — exact timestamps matter for HGN, where the duration and angle of observation affect clue validity.

Cross-examination targets include the officer’s exact wording of instructions (compared against the NHTSA script), the angle and distance of HGN stimulus movement, whether the officer demonstrated WAT before asking the subject to perform it, and whether environmental conditions were noted in real time or reconstructed later from memory.

Expert witnesses add significant weight in the right cases. An ophthalmologist can challenge HGN findings when the officer’s technique was imprecise. An occupational therapist or physical therapist can address balance-related confounders for WAT and OLS. A toxicologist can address the relationship between BAC, observed behavior, and the timing of testing.

Pro Tip: Video footage from body cameras and dash cameras is often subject to automatic deletion within 30 to 90 days, depending on the agency. A written preservation letter sent immediately after arrest, before any formal discovery request, is the single highest-leverage step you can take. An attorney who handles this on day one gives you options that simply do not exist if you wait.

For a broader look at DUI defense strategies in New Hampshire, Lydon Law’s guide covers the full range of approaches available to defendants.

If you were arrested after a poor FST performance: what happens next

The procedural path after a DWI arrest in New Hampshire moves on two parallel tracks: the criminal case and the administrative license action. Understanding both helps you respond quickly and protect your interests.

The typical sequence looks like this:

• Traffic stop and FST: Officer observes signs of impairment, requests FSTs, and forms a probable-cause determination.
• Arrest and chemical testing: If arrested, you are transported for an evidentiary breath or blood test under RSA 265-A:4. Results at or above 0.08% BAC for adults (0.02% for drivers under 21) trigger both criminal charges and administrative action.
• Booking: You are processed, and the officer submits a sworn report to the Department of Safety under RSA 265-A:30.
• Administrative license suspension: The DMV issues a notice of suspension based on the officer’s report. You typically have a limited window to request a hearing to contest this suspension.
• Arraignment: Your first court appearance, where charges are formally read and bail conditions are set.
• Pretrial process: Discovery, motions (including suppression motions targeting FST evidence), and plea negotiations occur in district court.

For a detailed breakdown of what a first-offense DWI means for your license and your record, Lydon Law’s page on first-offense DWI in New Hampshire covers the specific penalties and what to expect at each stage.

Typical cost categories in a DWI case include court fines, administrative fees, license reinstatement fees, ignition-interlock device installation and monitoring costs, increased insurance premiums, and attorney fees. Every case is different, and the total depends heavily on the facts, your prior record, and how the case resolves. An early consultation gives you a realistic picture of what you are facing.

Practical do’s and don’ts at the roadside

Knowing your rights in the abstract is one thing. Knowing what to say and do in the moment is what actually protects you. Here is a concise checklist:

Do:

• Stay calm and polite throughout the stop.
• Provide your license, registration, and proof of insurance when asked.
• State clearly that you decline to perform field sobriety tests.
• Ask whether the stop is being recorded by body camera or dash camera.
• Note the officer’s name, badge number, and patrol car number.
• Mentally record the time, location, road surface, and weather conditions.
• If arrested, immediately invoke your right to an attorney before answering questions or submitting to any testing beyond what implied consent requires.

Don’t:

• Volunteer information about where you were, what you drank, or how you feel.
• Attempt to perform FSTs if you feel unwell, are injured, or are on medication that affects balance.
• Argue with the officer or become confrontational.
• Assume that being cooperative means performing every test requested.
• Wait to contact an attorney until after your arraignment.

Two short scripts for the most common moments:

Declining FSTs: “Officer, I respectfully decline to perform field sobriety tests. I am not trying to be uncooperative.”

After arrest: “I am invoking my right to an attorney. I will not answer questions or perform any additional tests until I have spoken with counsel.”

Concrete steps to challenge FST evidence before and at trial

A strong FST defense in New Hampshire is built before the trial, not during it. Here is the step-by-step litigation roadmap that defense counsel follows:

1. Send a written preservation letter immediately. Address it to the arresting agency and any municipality that may hold footage. Request that all body-camera video, dash-camera video, and related electronic records be preserved pending litigation.
2. File a formal discovery demand. Request officer training records (SFST certification and refresher dates), all video footage, patrol notes, PBT calibration logs, evidentiary breath machine records, and the incident timeline.
3. Compare the officer’s report against NHTSA protocols. Every deviation from the scripted instructions or scoring criteria is a potential suppression argument or cross-examination point.
4. Evaluate suppression motions. If the stop itself lacked reasonable suspicion, or if the arrest lacked probable cause, a motion to suppress can exclude the FST observations and any evidence that followed.
5. Retain expert witnesses where the facts support it. HGN challenges benefit from ophthalmological expertise. Balance-test challenges benefit from a physical or occupational therapist. Toxicological testimony can address the relationship between BAC and observed behavior.
6. Prepare cross-examination on environmental conditions. For WAT and OLS, document the exact surface, slope, lighting, and weather at the time of the test. If the officer’s report omits these details, that omission is itself a cross-examination target.
7. Challenge officer qualifications and training recency. An officer whose SFST certification has lapsed or who has not completed required refresher training has a weaker foundation for their observations.

Specific documents and why each matters:

• Body-camera footage: Shows the actual instructions given, the subject’s performance, and the surface conditions. Often contradicts the written report.
• SFST certification records: Establish whether the officer was currently trained and certified at the time of the stop.
• Patrol vehicle logs: Can establish the officer’s location and timeline, which matters for HGN observation timing.
• Breath machine calibration records: Required for any challenge to post-arrest chemical test results.

For a full picture of how to defend criminal charges in New Hampshire, Lydon Law’s guide addresses the procedural and tactical options available at each stage.

Key Takeaways

Field sobriety tests in New Hampshire are voluntary, and the evidentiary weight of NHTSA-standardized tests depends entirely on strict protocol adherence and favorable conditions at the roadside.

Point	Details
FSTs are voluntary in NH	Refusing roadside physical tests does not trigger the license suspension that applies to chemical-test refusals under RSA 265-A:4.
NHTSA protocols are strict	HGN, Walk-and-Turn, and One-Leg Stand lose evidentiary weight when officers deviate from scripted instructions or ignore environmental conditions.
Confounders are common	Medical conditions, age, injury, footwear, and surface conditions can cause poor FST performance with no alcohol involved.
Preserve evidence immediately	Body-camera and dash-camera footage can be deleted within weeks; a written preservation letter sent on day one protects your defense options.
Lydon Law handles NH DWI defense	Attorney Kalie Lydon works directly with clients on FST challenges, discovery demands, and DWI representation throughout New Hampshire.

What the FST process looks like from the defense side

Most people assume that if they performed poorly on a field sobriety test, the case is essentially decided. That assumption is wrong, and it is one of the most consequential misunderstandings I see in DWI defense work.

The reality is that FST results are only as reliable as the conditions under which they were administered. A test conducted on a sloped shoulder at 2 AM in January, by an officer whose last SFST refresher was three years ago, with no video to verify the instructions given, is a very different evidentiary proposition than the controlled-condition validation studies suggest. Small procedural deviations change clue counts. Missing documentation creates reasonable doubt. Early preservation of video evidence has changed outcomes in cases where the written report told a very different story than the footage.

The content in this article is general information, not legal advice for your specific situation. If you are facing a DWI charge in New Hampshire, the facts of your case determine your options, and those facts need to be reviewed by an attorney promptly.

Lydon Law’s approach to DWI and FST defense in New Hampshire

Facing a DWI charge after a difficult roadside stop is stressful, and the decisions you make in the first days after an arrest shape what options remain available to you. Lydon Law’s criminal defense practice covers the full range of DWI defense work in New Hampshire: case evaluation, written preservation letters, formal discovery demands, expert witness coordination, suppression motion practice, and trial representation in district and superior courts throughout the state.

Attorney Kalie Lydon brings extensive courtroom experience to every case, including appearances before the New Hampshire Supreme Court. Clients work directly with Attorney Lydon throughout the process, not with paralegals or rotating staff. That direct relationship means your attorney understands the specific facts of your stop, your FST performance, and the evidentiary record from the first consultation forward.

If you were stopped, tested, or arrested for DWI in New Hampshire, contact Lydon Law for a case evaluation. The sooner you reach out, the more options remain open. This article provides general information and does not constitute legal advice for your individual circumstances.

Useful sources

These are the primary and authoritative sources that support the claims in this article:

• NHTSA DWI Detection and Standardized Field Sobriety Testing Participant Manual (2023) — the definitive source for SFST protocols, clue criteria, and administration requirements for HGN, WAT, and OLS.
• NHTSA SFST Refresher Participant Manual (2023/2024) — covers ideal-condition requirements and how environmental or procedural deviations affect evidentiary weight.
• NHTSA SFST Refresher Manual (legacy version) — supports points about officer training recency and the importance of strict protocol adherence.

FAQ

Are field sobriety tests mandatory in NH?

No. Field sobriety tests are voluntary in New Hampshire, and you may politely decline them without triggering the license suspension that applies to chemical-test refusals under RSA 265-A:4. Officers are not required to inform you of this right.

What is the legal BAC limit in New Hampshire?

The statutory BAC limit is 0.08% for adults and 0.02% for drivers under 21. These thresholds apply to chemical tests, not FST performance.

Does New Hampshire conduct sobriety checkpoints?

New Hampshire does not currently authorize sobriety checkpoints. DWI enforcement in the state relies on traffic stops based on observed driving behavior or equipment violations rather than checkpoint-based screening.

What happens if I refuse a chemical test in NH?

Refusing a post-arrest chemical test triggers administrative license suspension under RSA 265-A:30, separate from any criminal DWI charge. This is the implied-consent consequence, and it is distinct from declining a roadside FST.

How can Lydon Law help if I failed a field sobriety test?

Lydon Law evaluates the specific facts of your stop, sends preservation letters for video evidence, demands full discovery including officer training records, and challenges FST results through suppression motions and expert testimony in New Hampshire courts.

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