Police contact comes in levels, and two matter most: a detention (a brief stop) and an arrest (being taken into custody).
Each requires something different — and getting the line wrong is a common, and challengeable, police mistake.
The Levels of Contact
A consensual encounter is just talking — you are free to leave. A detention is a brief stop where you are not free to leave, and it requires reasonable suspicion. An arrest is a full seizure into custody, and it requires probable cause. See reasonable suspicion vs. probable cause.
Where the Line Is
The question is whether a reasonable person would feel free to leave. Handcuffs, a locked patrol car, drawn weapons, a long stop, and being moved can turn a ‘detention’ into a de facto arrest — which then needs probable cause, not just suspicion. Police sometimes hold someone as if arrested while claiming it was only a detention.
Why It Matters
If police arrested you (in substance) without probable cause, or detained you without reasonable suspicion, everything that followed — a search, a statement, a test — may be suppressible. A motion to suppress turns on exactly this line. It is one of the first things a defense lawyer maps out.
Frequently Asked Questions
What is the difference between a detention and an arrest?
A detention is a brief investigative stop where you are not free to leave, and it requires reasonable suspicion. An arrest is being taken into custody, and it requires the higher standard of probable cause. A consensual encounter, by contrast, is just talking — you are free to leave.
When does a detention become an arrest?
When a reasonable person would no longer feel free to leave and the intrusion resembles custody — handcuffs, a locked patrol car, drawn weapons, a prolonged stop, or being moved. At that point it is a de facto arrest that requires probable cause, not just reasonable suspicion.
Why does the detention-vs-arrest line matter?
Because if police arrested you in substance without probable cause, or detained you without reasonable suspicion, the evidence that followed may be suppressed. A motion to suppress often turns on exactly where that line falls.
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Ahmed S. Hasan
San Francisco Criminal Defense Attorney · State Bar of California #364992
Ahmed S. Hasan is the founder of ASH Legal, a solo criminal defense practice based in San Francisco. The firm runs on flat-fee representation: one lawyer, one fee, from arraignment through resolution. No hourly billing. No surprise invoices.
Ahmed is a graduate of Emory University School of Law and a member in good standing of the State Bar of California (Bar #364992). His practice focuses on San Francisco misdemeanor defense — DUI, domestic violence, petty theft and shoplifting, drug possession, vandalism, trespassing, and assault and battery — with particular attention to diversion-track outcomes that end in dismissal under PC 1001.95, PC 1001.36 (Mental Health Diversion), PC 1001.80 (Military Diversion), and PC 1001.83 (Parental Caregiver Diversion).
Ahmed previously served as a post-bar clerk with the San Francisco Public Defender's Office, the city's largest indigent-defense practice. He is a member of the Asian Pacific American Bar Association of Silicon Valley.
He represents clients at the San Francisco Hall of Justice (850 Bryant Street) and the Civic Center Courthouse. The ASH Legal office is at 15 Boardman Place, Suite 301, San Francisco, CA 94103.
Free 30-minute consultations are available by phone or Zoom. (510) 545-6515 · ahmed@ashlegal.com