In the United States, an arrest without a warrant still requires probable cause – in the case of an arrest without a warrant, probable cause must be promptly filed. An arrest without warrant is generally allowed when:
The person has committed a felony or misdemeanor, and the officer has witnessed it
A felony has been committed and the officer reasonably believes, known as probable cause, the person being arrested is the one who has committed it, as long as immediately after a warrant is obtained from the court.
When a suspect is in their home but one of the exigent circumstances occur; this is when an officer has reason to believe the suspect is escaping, evidence is being destroyed, and when a person inside is in danger of being harmed.
Section 24, as of January 1st 2006, provides that a constable may arrest, without a warrant, anyone who is about to commit or is currently committing an offence. The constable is also entitled to arrest anyone guilty of an offence or anyone who he reasonably believes to be guilty of an offence. However, the constable must have reasonable grounds that any of the following reasons make it necessary to arrest the person in question: to enable the real name or address of the person in question to be ascertained, or to prevent the person in question:
causing physical injury to himself/herself or any other person,
to protect a child or other vulnerable person from the person in question,
to allow the prompt and effective investigation of the offence or of the conduct of the person in question,
to prevent any prosecution for the offence from being hindered by the disappearance of the person in question.
Section 24A has similar provisions for citizens' arrests but the reasons permitted for arrest by anyone other than a constable are limited to preventing the person in question from causing injury to the arrestor, themselves or to others; preventing property damage; or preventing the person in question from making off before a constable can assume responsibility for him. The definition of an arrest, however, is contained in the judgement of Lord Diplock in Holgate-Mohammed v Duke, where he stated that an arrest is "a continuing act; it starts with the arrester taking a person into his custody,, and it continues until the person so restrained is either released from custody or, having been brought before a magistrate, is remanded in custody by the magistrate's judicial act." In the Philippine setting, a peace officer or a private person may, without a warrant, arrest a person: a. When, in his presence, the person to be arrested has committed, is actually committing, or is attempting to commit an offense; b. When an offense has just been committed and he has probable cause to believe, based on personal knowledge of facts or circumstances, that the person to be committed has committed it; c. When the person to be arrested is a prisoner who has escaped from a penal establishment or place where he is serving final judgment or temporarily confined while his case is pending, or has escaped while being transferred from one confinement area to another; d. Where the accused released on bail attempts to leave the country without court permission; e. Violation of conditional pardon, punishable under Article 159 of the Revised Penal Code as a case of evasion of service of sentence; and f. Arrest following a Deportation Proceeding by the Immigration Commissioner against illegal and undesirable means.
