Short answer. An arrest becomes the crime of unlawful arrest when someone seizes or detains another person in a case not authorised by law, or without reasonable ground, but does so intending to hand that person over to the authorities. The purpose of delivery is what separates this crime from illegal detention.
What the law says
shall be imposed upon any person who, in any case other than those authorized by law, or without reasonable ground therefor, shall arrest or detain another for the purpose of delivering him to the proper authorities
Revised Penal Code, Article 269 — Unlawful Arrest. Read the full provision →
The three things that must all be present
Article 269 of the Revised Penal Code punishes anyone who arrests or detains another person. First, there must be an actual arrest or detention — the person is physically taken or held, not merely accused or reported. Second, the arrest must fall outside the situations the law allows, or be made without reasonable ground. Third, and decisively, the person who made the arrest must have intended to deliver the one arrested to the proper authorities.
That third element is what defines the offence. Someone who grabs a person and locks him in a room out of spite is dealing with illegal detention. Someone who grabs a person on a groundless suspicion and marches him to the barangay hall or the police station is in the territory of Article 269.
The penalty today, after RA 10951
The penalty is arresto mayor together with a fine not exceeding One hundred thousand pesos (₱100,000). That peso figure is current only because of Republic Act No. 10951 (2017), which rewrote the fines and property values across the Revised Penal Code. Many books, websites and reviewers still print the 1930 amounts, which are far lower and no longer the law.
If you are reading a copy of the Code that gives a different fine for this article, check its date before you rely on it. Arresto mayor is a light penalty measured in months, but a conviction is still a criminal record, and the fine sits on top of it.
Private citizens and officers are both covered
The article speaks of any person. It reaches an ordinary private individual who makes a citizen's arrest on a hunch, a security guard who detains a suspected shoplifter with nothing to go on, and a barangay official acting outside the law's grounds. Peace officers who detain without legal ground are usually dealt with under the separate articles on arbitrary detention and delay in delivery, which exist precisely because a public officer's abuse of the arrest power is treated differently.
Good faith is not a blanket defence, but reasonable ground is written into the article itself. Where genuine, concrete circumstances pointed to the person arrested, the second element is not met.
If it happened to you or you are accused
Write down, as soon as you can, the date, time, place, who took hold of you, what was said, where you were taken, and how long you were held. Names of witnesses and any CCTV or phone footage matter far more than memory months later. Medical records help if you were hurt in the process.
A criminal complaint is not the only route — an unlawful arrest can also give rise to a separate civil claim for damages, and administrative liability where an officer is involved. Nobody can promise how a particular complaint will turn out. Bring your documents to a lawyer and get the charge assessed on the actual facts before filing anything.