First: If you are not under arrest (for example, it's just a detention or consensual encounter), the police need not advise you of your Miranda Rights (right to remain silent and right to counsel).  If you are not under arrest, it is up you to know and assert your right by clearly informing the officer that you are invoking your 5th Amendment Right to remain silent. If you do not know your rights and fail to assert them, then any questions you answer could be used against you and any question you fail to answer might also be used against you.  It is important that you know and immediately assert your right to remain silent.

Second: Once you are placed under arrest, the police are supposed to advise you of your Miranda Rights (right to remain silent and right to counsel).  If the officer fails to give you a Miranda warning, what you say cannot be used against you in the case in chief - however, it can be used for impeachment.  Thus, if you testify inconsistent with what you allegedly told the officer, that alleged statement could be used against you.

Third: Any statements found to have been forced or beaten out of you by the police cannot be used for any purpose.

Example: The police sometimes conduct criminal investigations by telephone. This eliminates any contention that your statement was forced or custodial, because you could easily end the conversation by hanging up.

Even seemingly exculpatory (or favorable) statements can be dangerous. Lets say a detective suspects you may have been involved in a bar fight, but cannot place you at the scene of the crime (the bar).  He calls you up and says he knows you were involved. You say “I was there, but not involved"  By placing yourself at the scene, the detective may now be able to get a court order for you to submit to a fingerprinting comparison of those left at the scene. Your statement can be used against you because the phone conversation was unprotected.

The routine gathering of background information is also not protected by Miranda. In other words, the police can ask someone who is in custody, questions that are not designed to lead to an incriminating response. Those answers can be used in court.

In a DUI investigation, your Miranda Rights and 4th Amendment Rights can be particularly confusing.

For example, if, during Field Sobriety Tests (FSTs), the officer asks you to recite the alphabet, does your right to remain silent apply (did you assert your rights)?

What if the officer asks you estimate 30 seconds in your head, and then tell him when you are done (should Miranda apply)?

What if the officer arrests you and asks you to pick a blood, breath or urine test?  How might that coincide with your Miranda Rights and your 4th Amendment Right not to consent to an unreasonable search [note that according to the United States Supreme Court in Missouri v McNeely (decided April 17, 2013) a blood draw is a presumptively unreasonable search and, absent exigent circumstances, a warrant is required].  Thus, one can assume a forced blood draw is unreasonable.

The more complicated questions is how anyone could possibly be expected to know whether there are sufficient facts to satisfy the exigent (emergency) circumstances exception to the 4th Amendment [i.e., because sufficient exigent circumstances can purportedly make a forced blood draw Constitutional (however, one thing we know is that the effervescence of alcohol alone is insufficient exigent circumstances to avoid the warrant requirement]? This is important because if you get it wrong and there were sufficient exigent circumstances, you could be charged with a refusal.

Thus, is the implied consent law Constitutional?

The best advice to anyone being questioned by the police about a crime is to immediately invoke their Miranda Rights and not answer any questions.  During a DUI investigation an officer may construe the assertion of your rights as being uncooperative (i.e., an indication of impairment) and they may refuse to respect your rights in such a way that asserting them becomes an insurmountable task.  At the very least, one should reserve all their rights to the fullest extent permissible under the U.S. and California Constitutions before allowing law enforcement to do anything other than what they are legally entitled to do.

As any prosecutor or defense attorney can tell you - the road to jail is paved with good confessions.