On rare occasion I will have a client who initially refuses the breath test at the station only to change their mind and demand the chance to "blow."  The relevant question is, under some circumstances, must the officer allow the driver to take the test? The answer is Yes, law enforcement must give drivers a "second" chance to test under the following limited circumstances: (1) within a very short and reasonable time after the prior first refusal; (2) when a test administered upon the subsequent consent would still be accurate; (3) when testing equipment is still readily available; (4) when honoring the request will result in no substantial inconvenience or expense to the police; and (5) when the individual requesting the test has been in the custody of the arresting officer and under observation for the whole time since arrest. In other words, the request must be made shortly after the initial refusal and while still in custody.  If the accused has bonded out of jail or placed in a jail cell and changes their mind concerning a breath test, the officer is not required to grant the request.  Ideally, the accused has an idea on whether to test before going out and drinking and driving.  The first question I get from clients is whether or not "to take the test" if stopped.  The answer depends on what state you are licensed in; what your history is regarding DUIs; and how aggressive you might be in challenging the case.  I can not give a definitive answer to this question without a brief interview of the client.  As a general rule, a refusal of the test triggers an extended suspension of your license, ie one year, whereas a "failure" of the test (over .08) will cause a 30-day suspension in Missouri and Kansas (unless the test exceeds 0.15).  I have addressed each of these issues in more detail on my site.