Many factors contribute to a police officer's level of authority in a given situation. Understanding the what, when, why, and how of police conduct during a stop is confusing for most people. Varying standards of proof exist to justify varying levels of police authority during citizen contacts. While Know My Rights maintains that it is never a good idea to consent to a search or to answer incriminating questions, a working knowledge of these standards will help the citizen better understand when police can surpass constitutional protections.
A police officer has "reasonable suspicion" when there exists articulable facts or circumstances which would lead a reasonable person to suspect that a crime has been, is being, or will be committed.
At this stage, police may detain the suspect for a brief period and perform a frisk. In some cases, drug-sniffing dogs may be called to the scene, although officers must cite a specific reason for suspecting the presence of drug evidence. Refusing a search does not create reasonable suspicion, although acting nervous and answering questions inconsistently can. For this reason, it is best not to answer questions if you have to lie in order to do so. Police authority increases if they catch you in a lie, but not if you refuse to answer questions. As a general rule, reasonable suspicion applies to situations where police have reason to believe you're up to something, but they don't know what it is.
A police officer has "probable cause" when there exists articulable facts or hard evidence that would lead a reasonable person to believe that a crime has been, is being, or will be committed and the person under investigation is the one responsible for the crime.
At this stage, police may perform a search, and often an arrest. Probable cause generally means police know what crime they suspect you of and have discovered evidence to support that belief. Common examples include smelling or seeing evidence in plain view, or receiving an admission of guilt for a specific crime.
For the conscientious citizen, the best advice regarding police authority is to stick to your guns and not waive your constitutional rights under any circumstances. Police officers will often give misleading descriptions of what their authority is, but you have nothing to gain by submitting to coercive police tactics. Police must make ad hoc decisions regarding their authority level in a given situation and these decisions are subject to review in court. Asserting your rights properly is good way to avoid arrest, and it is an even better way to avoid a conviction.