4th Amendment and Cell Phones: Riley, Warrants, and Exceptions

Under the Fourth Amendment, police generally cannot search the digital contents of a cell phone without a warrant supported by probable cause, even when they arrest you and take the phone off you at the scene. The Supreme Court settled that rule in 2014 in Riley v. California, treating the smartphone in your pocket as fundamentally different from a wallet or a bag.¹ A handful of narrow exceptions exist, and knowing where they end is what separates evidence a judge will admit from evidence a judge will throw out.

The Warrant Requirement Under Riley

In Riley, the Court unanimously rejected the practice of searching phones under the “search incident to arrest” doctrine that lets officers examine items found on someone they’re arresting. Digital data is different. A single phone can hold millions of pages of text, thousands of photos, and years of location history, and the Court concluded that phones hold “the privacies of life.”¹ Searching one is a far greater intrusion than emptying a pocket.

The physical device is treated separately. Officers can still inspect the hardware during an arrest to check for hidden weapons, like removing a case to look for a razor blade. What they cannot do without a warrant is tap the screen and start reading your messages.

Police Can Hold Your Phone While They Get a Warrant

Riley does not require officers to hand the phone back while they apply for a warrant. The Court explicitly said police can seize and secure a phone to prevent destruction of evidence during the wait, calling that “a sensible concession.”¹

The Court also addressed remote wiping, the risk that someone could erase a seized phone’s data from another device. It pointed to two countermeasures: turning the phone off, or placing it in a Faraday bag, a simple enclosure that blocks radio signals. Many agencies already carry Faraday bags as standard equipment. So in practice, if police take your phone lawfully, expect them to isolate it from the network and keep it until a magistrate signs off.

When Police Can Search a Phone Without a Warrant

The warrant rule is the default, not an absolute. The Court in Riley acknowledged that other recognized exceptions still apply to phones, and each one has boundaries worth understanding.

Consent

If you voluntarily agree to a search, officers don’t need a warrant. Courts examine the totality of the circumstances to decide whether consent was freely given or coerced.² Threats, intimidation, or deception that overbear your will can invalidate consent. You are not required to say yes, and refusing cannot be used against you.

Consent can also be withdrawn. If you initially agree and then change your mind, you can revoke consent and the search must stop. Courts have held that once consent is pulled before officers actually examine the data, any further search violates the Fourth Amendment, even if police already copied the phone’s contents. If you consented and regret it, say so clearly and immediately.

Exigent Circumstances

When a real emergency exists, police can act without a warrant. The Riley Court listed examples: preventing imminent death or serious injury, stopping the destruction of evidence in a specific case, or pursuing a fleeing suspect.¹ A vague worry that evidence might disappear at some point does not qualify. The emergency has to be immediate, and officers who invoke it will have to justify the claim to a judge later.

Plain View

If an officer is lawfully holding a phone and incriminating information appears on the screen without the officer manipulating the device, the plain view doctrine may apply. A text notification popping up on a locked screen during a property inventory is the standard example. The officer didn’t unlock the phone, open an app, or press a button. This remains a murky area, and the safer legal position is that any deliberate interaction with the phone crosses into a search that requires a warrant.

Border Searches

Federal agents at international borders and their functional equivalents, including international airport terminals, have broader authority to inspect travelers and their electronic devices.³ CBP policy splits these into two levels:

A basic search, where an officer manually scrolls through the device without connecting external equipment. CBP can conduct these without any suspicion.
An advanced search, where an officer connects equipment to copy or forensically analyze the device. This requires reasonable suspicion of a legal violation or a national security concern, plus approval from a senior manager.

The distinction matters because an advanced forensic search can pull deleted files, metadata, and data you didn’t know was there. Reasonable suspicion is a lower bar than the probable cause needed for a warrant, but it still means CBP cannot forensically image every traveler’s phone at random.³

Location Records and Cloud Data

Not everything the government wants from your phone lives on the phone. Two other categories matter: the location trail your carrier logs, and the files you store in the cloud.

In 2018, the Court extended Riley’s logic to historical cell-site location information in Carpenter v. United States. Every time your phone connects to a tower, your carrier records which tower handled the call, and over months those logs reconstruct where you’ve been within roughly 50 meters. The Court held that accessing that data is a Fourth Amendment search and requires a warrant.⁴ The government in that case had obtained 127 days of Carpenter’s location records from his wireless carrier under a Stored Communications Act order that required less proof than a warrant. That wasn’t enough.

Carpenter also cut into the third-party doctrine, the older principle that information you voluntarily share with a company loses Fourth Amendment protection. The Court refused to apply that doctrine to CSLI, reasoning that phones log location automatically and opting out would mean not carrying a phone at all.⁴ The ruling was written narrowly and did not overturn the doctrine as a whole.

Cloud storage sits in a grayer zone. When your photos, messages, or documents live on services like iCloud, Google Drive, or Dropbox, police have two paths: search the phone under Riley, or serve legal process on the company. Under the Stored Communications Act, a warrant is generally required for the contents of communications, while metadata like subscriber information can sometimes be obtained with a subpoena or court order. Whether the third-party doctrine still applies to broader categories of cloud-stored data after Carpenter is an evolving question in the lower courts.

Can Police Force You to Unlock the Phone?

Even with a valid warrant, officers face a practical wall: modern phones are encrypted. Whether they can compel you to unlock yours depends on how it’s locked, and the answer turns on the Fifth Amendment rather than the Fourth.

Courts have generally held that a passcode is testimonial, because forcing you to produce it means forcing you to reveal the contents of your mind. You cannot be compelled to tell police your password.

Biometric unlocking has been treated differently, but the law is now genuinely unsettled. For years, most courts viewed pressing a finger to a sensor as a physical act more like providing a handwriting sample. That shifted in January 2025, when the D.C. Circuit ruled in United States v. Brown that compelling a suspect to unlock his phone with his thumbprint violated the Fifth Amendment. The court reasoned that the act itself communicates knowledge: that you own the phone, that you can access it, and that you know how. The Ninth Circuit has gone the other way, treating biometric unlocking as closer to routine fingerprinting. The Supreme Court has not resolved the split, so the answer depends on where you are. Powering the phone off before an encounter forces it to require a passcode on next startup, and biometrics alone won’t get past that.

A Note on Parole and Probation

The Riley warrant requirement applies in full to most people, but not to everyone. Courts have consistently held that people on supervised release have a diminished expectation of privacy, and their phones can often be searched on less justification.

For probationers, the standard is typically reasonable suspicion. Many supervision agreements include explicit consent clauses requiring the person to submit to unannounced searches of their electronic devices. For parolees, the Supreme Court in Samson v. California upheld a California law authorizing entirely suspicionless searches, on the theory that parolees’ privacy expectations are severely reduced as a condition of release.⁵ Most jurisdictions still require at least reasonable suspicion in practice, but the constitutional floor is lower than many people expect.

Remedies When Police Search Illegally

If police search your phone without a warrant and no exception applies, the main remedy is the exclusionary rule: evidence found during the unconstitutional search cannot be used against you in court. A defense attorney raises this through a motion to suppress, and if the judge grants it, the prosecution loses access to whatever the search turned up.

The rule reaches further than the direct evidence. Under the “fruit of the poisonous tree” doctrine, evidence discovered only because of the initial illegal search is also inadmissible. If officers illegally read your texts, found a co-conspirator’s name, and used that name to build a separate case, the whole chain can be suppressed.

The exclusionary rule has an important limit. In United States v. Leon, the Supreme Court held that evidence obtained by officers acting in reasonable reliance on a warrant later found invalid is still admissible.⁶ This good-faith exception does not apply if the officer misled the judge to get the warrant, or if the warrant was so obviously deficient that no reasonable officer would have relied on it.

You may also have a civil remedy. Under 42 U.S.C. § 1983, someone acting under government authority who deprives you of a constitutional right can be held liable in damages.⁷ Officers are shielded by qualified immunity, which protects them unless their conduct violated clearly established law. After Riley, the warrant requirement for phone searches is about as clearly established as Fourth Amendment law gets, so a blatantly warrantless phone search is a weaker candidate for immunity. Cases involving disputed facts or new questions, like whether viewing a lock-screen notification is a search, give officers more room to argue the law wasn’t clear enough.

Do Not Wipe a Seized Phone

Some people’s instinct when police take a phone is to remotely wipe it. That is a serious mistake. Destroying records relevant to a federal investigation can be prosecuted under 18 U.S.C. § 1519, which reaches anyone who knowingly destroys or conceals a record or tangible object to obstruct a federal matter. The penalty is up to 20 years in prison, potentially far worse than the underlying investigation. State evidence-tampering laws carry their own penalties, and prosecutors have brought these charges. The Riley Court treated remote wiping as a technical problem for police to solve, not a right you can exercise. Once your phone has been lawfully seized, attempting to erase the data does not usually work, and it creates a new criminal charge on top of whatever the original one was.

1
Justia U.S. Supreme Court Center. Riley v. California, 573 U.S. 373 (2014)
2
Legal Information Institute. U.S. Constitution Annotated – Consent Searches
3
U.S. Customs and Border Protection. Border Search of Electronic Devices at Ports of Entry
4
Justia U.S. Supreme Court Center. Carpenter v. United States, 585 U.S. 296 (2018)
5
Justia U.S. Supreme Court Center. Samson v. California, 547 U.S. 843 (2006)
6
Justia U.S. Supreme Court Center. United States v. Leon, 468 U.S. 897 (1984)
7
Office of the Law Revision Counsel. 42 U.S. Code 1983 – Civil Action for Deprivation of Rights