Field sobriety tests (FSTs) are a group of physical and cognitive tests that officers perform at the roadside to judge if a driver is impaired. These tests are standardized by the National Highway Traffic Safety Administration (NHTSA) and include:

- Horizontal Gaze Nystagmus (HGN) Test: The officer watches the driver’s eyes while they follow a moving object, looking for an involuntary jerking motion indicating impairment.
- Walk-and-Turn Test: The officer tells the driver to walk in a straight line, heel to toe, turn, and come back, and then assesses balance, coordination, and ability to follow instructions.
- One-Leg Stand Test: The driver must stand on one leg and count aloud to check balance and concentration.

The problem with field sobriety tests is that they are subjective, based on the officer’s judgment, and can result in arguments about their accuracy.

Field sobriety tests are more objective than chemical tests and give scientific evidence of impairment. These tests measure the driver’s BAC or the presence of drugs using one or more methods:

- Breath Tests: A breathalyzer measures the amount of alcohol in a driver’s breath and serves as an estimate of the driver’s BAC. These can take place at the roadside or police station.
- Blood Tests: A laboratory analyzes blood samples to determine precisely how much alcohol or drugs are in the bloodstream. Blood tests are very accurate and take longer to process.
- Urine Tests: These are less commonly used to detect the presence of drugs or alcohol. Blood or breath tests are generally considered more reliable than these.

Results from chemical tests are commonly admitted as evidence in DUI cases. However, these tests aren’t always accurate, and things like improper calibration, procedural errors, or medical conditions can influence them.

Almost all states have implied consent laws, which means that you consent to chemical testing when you get a driver’s license and are suspected of DUI. Refusing a chemical test can result in immediate penalties, including:

- License suspension: Refusal may result in an automatic suspension of driving privileges from 6 months to 1 year for a first offense.
- Fines and fees: If you refuse, you can be fined and have to pay court fees. 
- Enhanced penalties: Refusal may lead to harsher penalties if convicted of DUI, as refusal is often considered an admission of guilt.

Field sobriety and chemical tests are not perfect, however, and can be challenged in court. Common defenses include:

- Improper administration: Field sobriety tests must be conducted according to standardized protocols. Deviations can undermine their validity.
- Medical conditions: Conditions such as neurological disorders or injuries can affect test performance and mimic signs of impairment.
- Faulty equipment: Breathalyzers and other testing devices must be calibrated and maintained correctly. Defective equipment can produce inaccurate results.
- Procedural errors: Officers must follow specific procedures when giving chemical tests. If they violate the protocols, the results are inadmissible.

An experienced DUI attorney can review your case's facts and spot essential weaknesses in the evidence that the prosecution has against you.

If you have been arrested for DUI, an experienced attorney can make all the difference in how your case turns out. Talk to a DUI attorney today to determine your legal rights and options.