Carpenter v. United States and the Trail of Data Every Phone Leaves

Timothy Carpenter was not the sort of defendant who usually changes constitutional law. Prosecutors said he helped organize a string of armed robberies at electronics and cell phone stores in Michigan and Ohio around 2010 and 2011, and a jury convicted him. The evidence that tied him to the scenes, though, did not come from fingerprints or eyewitnesses alone. It came from his phone company. Investigators had obtained months of records showing which cell towers his phone connected to, and so roughly where he had been, without ever asking a judge for a warrant. On June 22, 2018, the Supreme Court ruled that this was a search under the Fourth Amendment. In most cases, the Court said, the government needs a warrant to get those records. The decision was narrow on purpose. Its logic is not narrow at all, and the eight years since have been an argument about how far it reaches.

In short: Carpenter v. United States held that collecting a person's historical cell-site location records is a Fourth Amendment search that generally requires a warrant, rejecting the idea that sharing data with a phone company gives up all privacy in it. The Court left many questions open, from real-time tracking to data brokers. A 2026 ruling on Google location data extended the line, but much of your digital trail still sits in gray territory.

What a cell-site record is

Every time a phone connects to the network, to make a call, send a text or simply check for messages, it talks to a nearby cell tower. Carriers keep records of those connections for business reasons: billing, network planning, roaming charges. Each record shows which tower, and often which side of the tower, handled the connection at a given time.

One record says little. Thousands of them sketch a life. In Carpenter's case, prosecutors obtained 127 days of records from one carrier and a shorter period from another. The Court's opinion noted that the records produced nearly 13,000 location points, an average of about 101 a day. Strung together, they show where someone sleeps, works, worships and visits, and with whom they spend time.

As phones and networks have improved, those records have grown more precise. Towers have become denser in cities, so a connection can place a phone within a small area. And phones generate far more connections than they did a decade ago, because apps reach the network constantly in the background.

How investigators got the records

The government did not need a warrant under the statute it used. The Stored Communications Act, passed in 1986, lets prosecutors get certain phone records with a court order if they show "specific and articulable facts" that the records are relevant and material to an ongoing investigation. That is a lower bar than probable cause, which is what a warrant requires.

The government's legal position rested on the third-party doctrine. Under two decisions from the 1970s, United States v. Miller and Smith v. Maryland, information a person voluntarily hands to a business, such as bank records or dialed phone numbers, carries no reasonable expectation of privacy. Carpenter's location records were the phone company's business records, the argument went, and he had shared his location with the carrier simply by carrying a phone that was turned on.

The Sixth Circuit Court of Appeals agreed. The Supreme Court did not.

What the Court held, and how close it was

Chief Justice John Roberts wrote for a 5 to 4 majority, joined by Justices Ruth Bader Ginsburg, Stephen Breyer, Sonia Sotomayor and Elena Kagan. He drew on two lines of cases. One protected people against long-term tracking of their movements: in a 2012 GPS case, several justices had said that monitoring a person's car for weeks violated reasonable expectations. The other was the third-party doctrine. Cell-site records sat at the intersection, and Roberts concluded that the privacy interest won.

His reasons are worth knowing, because they are the ones lawyers now apply to other data. Cell-site records provide an intimate window into a person's life. They are detailed, encyclopedic and effortlessly compiled. They reach back in time, so police can reconstruct where anyone was on a given day long before anyone suspected them. And the sharing is not voluntary in any meaningful sense: carrying a phone is close to a necessity of modern life, and the phone logs its location without the user doing anything.

The Court held that accessing seven days of records was enough to count as a search, and it said the government must generally get a warrant supported by probable cause. Exceptions still apply in emergencies, such as a kidnapping or an imminent threat.

Every one of the four dissenters wrote separately. Justice Anthony Kennedy, joined by Justices Clarence Thomas and Samuel Alito, argued that the records belonged to the carrier, that the third-party doctrine plainly applied and that the majority had created confusion. Justice Alito warned the decision would unsettle the use of subpoenas for business records generally. Justice Thomas questioned the whole reasonable-expectation framework. Justice Neil Gorsuch took a different route, suggesting that people may have property rights in data held by others and that the Court should consider that approach instead.

What the Court left open

Roberts called the decision narrow and listed what it did not decide. It did not address real-time tracking of a phone's location. It did not address tower dumps, which are records of every phone that connected to a particular tower during a window of time. It did not call into question conventional surveillance tools such as security cameras. And it did not disturb the third-party doctrine for business records that might incidentally reveal location, such as bank records.

Those caveats were deliberate. The Court was writing about a technology that changes fast, and it chose not to issue rules for cases not in front of it. The cost of that caution is uncertainty. Since 2018, lower courts have disagreed on how Carpenter applies to tower dumps, to pole cameras watching a home for months, to license-plate readers and to records from apps.

A fair point on behalf of the dissenters: uncertainty has real costs for police too. Investigators acting in good faith may not know which records require a warrant. In Carpenter's own case, the evidence was ultimately allowed to stand under the good-faith exception, because officers had followed the statute as it existed. The decision protected everyone except the man who brought it.

Geofences and the 2026 decision

The biggest open question for years involved geofence warrants. Instead of asking where a known suspect was, police would draw a box around a crime scene and ask Google for location data on every device that was inside it during a window of time. Google stored location history for many users, and for a time police sent the company thousands of these requests a year.

Geofences invert ordinary policing. They start with everyone and work toward a suspect. Defense lawyers argued they were the kind of general search the Fourth Amendment was written to forbid. Prosecutors argued that users had opted in to Google's location history and that the warrants were reviewed by judges.

In June 2026, the Supreme Court decided Chatrie v. United States, a case arising from a 2019 bank robbery in Virginia. Writing for the Court, Justice Kagan held that getting a person's cell-phone location data from Google is a Fourth Amendment search. That confirms Carpenter's reasoning reaches beyond phone carriers to the companies that run the apps and services on the phone. Exactly what warrants for such data must say, and how broad they may be, is a question lower courts will keep working out. Google, for its part, changed in recent years how it stores location history, moving much of it onto users' own devices, which reduces what the company can hand over.

The data broker loophole

The largest gap Carpenter left is commercial. Countless apps collect location data and sell it, directly or through brokers, to anyone willing to pay. Federal agencies have bought such data, reasoning that a purchase is not a search because no one compelled anyone to hand it over. Reporting and government disclosures over the past several years have shown agencies from immigration enforcement to the military buying commercially available location and other data.

If that reasoning holds, the warrant rule in Carpenter can be avoided with a credit card. Civil liberties groups on the left and libertarian groups on the right have both pressed Congress to close the gap. A bill called the Fourth Amendment Is Not For Sale Act, which would bar law enforcement and intelligence agencies from buying certain data about Americans without legal process, passed the House in April 2024 with support from both parties. It did not become law.

Here is the argument this post makes: Congress should not wait for a court case to settle the broker question. The Supreme Court decides cases one at a time, years after the technology arrives. A statute can require a warrant for location data no matter how the government gets it, apply to all agencies and take effect at once. It is the rare civil liberties question with real allies across the aisle.

Shrinking the trail you leave

The law moves slowly, and in the meantime people can reduce how much location data exists about them. None of this is a substitute for legal protection, and none of it makes anyone invisible. Your carrier still knows which towers your phone uses as long as it is on the network. But much of the most detailed tracking comes from apps, and that part is within reach. What follows is general information, not advice for any particular situation, and the exact menus differ by phone and software version.

Review which apps can see your location. Both major phone operating systems let you see every app with location access and change it to "never," "only while using" or "ask each time." A weather app can usually work with an approximate location; a game rarely needs any.

Turn off precise location where it is not needed. Recent versions of both systems let you give an app only an approximate area rather than an exact point.

Check your account's location history. Google and Apple both offer settings that control whether your movements are saved to your account or kept on the device, and both let you delete past records. If the data is not stored on a company's servers, it cannot be handed over from there.

Limit advertising identifiers. Phones assign an identifier that apps use to link your activity for advertising. You can limit or reset it, which makes it harder for data brokers to build a profile.

Think about context. People attending a protest, visiting a sensitive clinic or meeting a source sometimes leave their phones behind or switch them off. That is a personal choice, and a legal right.

The point of listing these steps is not to put the burden on individuals. It is to show how much of the trail is a design choice by companies, which is exactly why the law should set rules rather than leaving each person to manage dozens of settings alone.

Why this matters for people who are not suspects

It is easy to think of the Fourth Amendment as a protection for criminal defendants. That misses who is most exposed. Location data can show who attended a protest, who visited a reproductive health clinic in another state, who went to a mosque or an immigration lawyer's office. People with the least power are often the most tracked and the least able to fight back.

Consider also how the data gets used after the fact. A location history collected for one investigation can sit in a file for years, available for purposes nobody imagined when it was gathered. Records that place someone near a crime scene can also place them at a union meeting, a doctor's office or a friend's house. The more data the government can gather without a judge's approval, the more those incidental details pile up about people who were never accused of anything. Carpenter's reasoning recognized that the scale of modern data changes the stakes of a search: what was once a single observation by a detective on the street is now a complete record of movement, retrievable in an afternoon.

A warrant requirement does not stop investigations. It puts a neutral judge between the government and a person's life, and it requires a reason before the search, not after. That is the whole design of the Fourth Amendment, and Carpenter applied it to a world its framers could not have pictured.

What you can do

Digital privacy is decided in courtrooms and in Congress. These tools help you keep watch on both:

• Read the opinions as they arrive. Court Watch carries the Supreme Court's opinions this term with the Court's own summaries, plus the emergency docket and the Senate's votes on judges. The judges confirmed now will decide the next Carpenter.
• Ask your lawmakers about the broker loophole. Put your address into find your representatives and you will see who represents you in Congress and in your state capitol, how to reach each office and what they voted on most recently. Ask whether they would require a warrant before any agency buys Americans' location data.
• Track the bill if it returns. The Congress votes and bills page follows votes and legislation, so you can watch for data-purchase limits in the new Congress that convenes in January 2027.
• Keep up with the courts. The courts topic page gathers reporting on the judges and cases shaping surveillance law.