Texas's "implied consent" law requires all drivers lawfully arrested for a DWI to submit to chemical testing to determine blood alcohol concentration (BAC) or the presence of drugs in the driver's system. (Texas used the term "DWI" instead of "DUI".) For an arrest to be lawful, the officer who stops you must have probable cause to believe you've been driving under the influence of alcohol or drugs.
The officer gets to decide which type of test—blood or breath—you must take. But once you submit to the officer's test, you have the right to have a blood test taken within two hours of your arrest by a medical professional of your choice (and at your own expense).
Normally, an officer cannot force you to take a test: If you decide not to submit to testing, you'll face consequences, but the officer must respect your choice. However, BAC testing mandatory if you:
An arresting officer is required by law to explain the consequences of refusing a test—that you'll be fined, lose your license, and face jail time if convicted of a DWI. The officer must also explain you don't have the right to speak to an attorney prior to taking the test and that a test refusal can be used against you in court.
Generally, the implied consent law doesn't require drivers to submit to chemical test prior to a lawful arrest. However, to establish probable cause to make an arrest, an officer might ask you to take a voluntary "preliminary alcohol screening" (PAS) test. A PAS test is typically administered with a handheld breath test device (often called a "breathalyzer") at the roadside.
The penalties for refusing to take a chemical test start at a 180-day license suspension. You could lose your license for two years if you refuse a test you've had at least one alcohol or drug-related "enforcement contact" within the last ten years. DWI convictions, BAC test refusals, and failed BAC tests all counts are prior enforcement contacts.
The wisdom of refusing a post-arrest chemical test depends on the circumstances. And refusal may not help you avoid a conviction—you can be found guilty even without test results. In fact, the prosecution can argue to a jury that your refusal shows consciousness of guilt—that you refused to test because you knew you were intoxicated.
If you've been arrested for DWI in Texas or any other state, get help from an experienced DWI attorney. A DWI conviction—especially one involving physical injuries or repeat offenses—carries serious consequences. So your best bet is to find an attorney who knows the law and your local court system.