When stopped for DWI, it used to be that you should simply refuse everything. Refuse the field sobriety tests, refuse the breath test, refuse the blood test, say as little as possible and ask for a lawyer. Assuming you had more than a few, this used to be a good plan (if you really only had two beers, you should probably be giving a blood test).
With the advent of search warrants for blood in DWI cases, this old paradigm can now end up making you much worse off. In Austin, Texas, where our practice is located, this started with “no refusal” weekends. APD started designating certain holidays or events (July 4 Weekend, Memorial Day Weekend, SXSW, etc.) as “no refusal” weekends. On “no refusal” weekends, if DWI arrestees did not give breath tests, the arresting officer would apply for a search warrant to take their blood. Over time, APD’s guidelines for when to get a search warrant for blood have gradually broadened outside of only “no refusal” weekends and holidays.
Currently, if you are stopped by APD for DWI and refuse any of their field sobriety tests—including the portable breath test (if one is available)—they will typically apply for a search warrant for blood. This is only absolute if there is a DWI enforcement officer involved. If there is not a DWI enforcement officer involved, depending upon the circumstances, you may still avoid a search warrant (for example: If you are stopped by an officer with less than 2-years experience, he or she will handle the arrest instead of calling for a DWI enforcement backup. Typically they will not get a search warrant even if you refuse some or all of the tests). If you have prior conviction for DWI, or if there is a collision, they will usually apply for a warrant even if you cooperate.
So, the game now is to avoid a search warrant for blood. Your best shot at this is to cooperate and perform all of the field sobriety tests (eye test, walk and turn, one leg stand and sometimes the modified Rhomberg test), and also to give a portable breath test if requested. Portable breath test results are not admissible in court, but they don’t always inform you about this (it is admissible for them to say it showed you had alcohol in your system, but they can’t say the number). If you are lucky, this will give you the best chance to avoid a search warrant for blood.
The rationale for this change in conduct is simple: Doing the field sobriety tests does give them ammunition to use against you, but poor balance is much easier to explain to a jury than a blood test where you are 2x the legal limit.
If it’s a “no refusal” day, you can’t get out of a search warrant for blood unless you give a breath test, so you may as well give a breath test. Breath tests are more susceptible to error than blood tests and, accordingly, easier to get jurors to bring into question.