Many people believe that if they are arrested and not "read their rights," they can escape punishment. Not true. But if the police fail to read a suspect their Miranda rights, the prosecutor can't use for most purposes anything the suspect says as evidence against the suspect at trial. Of course, as with nearly all legal rules, there are exceptions (such as where public safety is at issue).
The Miranda warning (from the U.S. Supreme Court's Miranda v. Arizona decision) requires that officers let you know of certain rights after your arrest and before questioning you. An officer who is going to interrogate you must tell you that:
It doesn't matter whether an interrogation occurs in a jail, at the scene of a crime, on a busy downtown street, or in the middle of an open field: If a person is in custody (meaning, they're not free to leave), the police must read the Miranda rights if they want to ask questions and use the answers as evidence at trial.
If someone is not in police custody, however, no Miranda warning is required and anything the person says can be used at trial. Police officers often avoid arresting people—and make it clear to them that they're free to go—precisely so they don't have to give the Miranda warning. Then they can arrest the suspect after getting the incriminating statement they wanted all along. (For more detail, see our article on the meaning of "custodial interrogation.")
Do you have to respond to police questions if you haven't been arrested? Generally, no. You typically don't have to answer even if you are under arrest. A police officer generally cannot arrest a person simply for failure to respond to questions. There are, however, situations where you might have to provide information like identification.
Beyond identifying who you are, you can tell the officers you're invoking your right to remain silent and would like to speak to an attorney. Although easier said than done (given it's a police officer), the almost-universal advice of defense attorneys is to keep the old mouth tightly shut when being questioned by police. Suspects all too frequently unwittingly reveal information that can later be used as evidence of their guilt. After consulting an attorney, you can make informed decisions on how to proceed and answer police questions.
Without a Miranda warning, what the arrestee says in response to custodial questioning can't be used for most purposes as evidence at trial. This rule—called the exclusionary rule—aims to deter police from questioning a suspect without informing them of their rights.
But that doesn't mean an un-Mirandized statement is completely off limits in the criminal case. While the prosecution can't use it to prove the crime, the statement can be introduced for other purposes, such as to attack the suspect's credibility. For more detail, see our article on when statements obtained in violation of Miranda can be used against you.
The Miranda rule is complex, and no one article can address all its ins and outs. If you've been arrested or charged with a crime, you should talk to a lawyer for a full explanation of the law, including how it may differ slightly in your state.