Under the Fourth Amendment to the United States Constitution, citizens are protected from “unreasonable” searches and seizures. This includes requiring a driver to take a blood or breath test. Over the years, courts have described what constitutes an unreasonable search or seizure. In general, police must have a search warrant in order to show that a search is reasonable. However, police can conduct a search under certain limited circumstances without a warrant.
Clearly, police officers are not able to obtain a warrant when they witness someone commit a crime. Therefore, courts have determined that if a police officer has probable cause to believe that someone has broken the law, the officer can stop and arrest them.
Sometimes, however, police officers have a belief that a crime has been committed, but cannot be sure. In these situations, a police officer can stop a citizen, ask them questions, and conduct an investigation so long as they have reasonable suspicion that the person has committed, is committing, or is about to commit a crime. In order to justify this type of stop, an officer must be able to point to articulable facts supporting the officer’s belief that the person stopped was involved in criminal activity.