To protect the rights of innocent citizens, the police must follow certain legal requirements before and during a lawful arrest and detention. These rules kick in to effect before the police approach you, after they take you into custody and even after you are placed in a jail cell. These important legal rules help provide a balance between maintaining public safety and respecting the private rights of citizens.
In most cases, the police must have an arrest warrant before they can detain you, or take you into custody. Judges sign warrants, but only after the police provide evidence sufficient to find "probable cause." Probable cause basically means it reasonably appears more likely than not that you have committed or will commit a crime. Sometimes the police can arrest without a warrant. For instance, when they personally witness you committing a crime, they can immediately arrest you. Police can also arrest without a warrant if they have probable cause to believe that an immediate arrest is necessary to prevent the commission of a crime.
An arrest warrant (or probable cause) is enough to begin an arrest, but it is not all that is required. To lawfully carry out an arrest, the police must take certain steps that inform you of your legal rights. First, the police must inform you of your Miranda rights, which generally include the right to remain silent and the right to consult with an attorney. And if you do request an attorney, the police cannot ask you any additional questions until your attorney is present. Then, the police must take you to a jail and carry out a formal "booking" procedure, where they gather your personal information, including footprints, and fill out the required paperwork about your arrest.
The U.S. Constitution requires that the police put you in front of an impartial, unbiased judge within four days after they arrest you. The judge will review the evidence against you, allow you to plead innocent or guilty, then will determine whether there is sufficient evidence to keep you in prison. Most of the time, the judge will set bail or bond. If you pay the bail or bond, you will be free to leave until your trial and, assuming you show up at trial, you will recover the money you put up for bond.