Cell site location information, often shortened to CSLI, is the record a wireless carrier keeps of which cell towers your phone connected to and when. Since the Supreme Court’s 2018 ruling in Carpenter v. United States, law enforcement generally needs a warrant supported by probable cause to obtain seven or more days of historical CSLI. How far back investigators can actually reach depends on the carrier: Verizon stores CSLI for roughly one year, T-Mobile for up to two years, and AT&T keeps certain location-linked records for up to five years. No federal statute sets a minimum retention period, so timing often decides whether the evidence still exists when anyone comes looking.
What CSLI Actually Shows
A powered-on phone constantly searches for the strongest nearby tower signal. Each time the device connects, the carrier logs the tower’s identity, the sector (the direction of the signal), and the start and end time of the connection. Most towers split their coverage into three sectors covering roughly 120 degrees each, so the carrier can estimate which direction the phone sat relative to the tower.
In dense urban areas with closely spaced towers, these records can place a phone within a few hundred feet. In rural areas, a single coverage arc might stretch for miles. The data also captures movement. As a person travels, the phone drops one tower and picks up the next, creating a chain of entries that trace a rough path. None of this requires the user to make a call or open an app. The phone generates these records automatically just by staying on.
When Police Need a Warrant for CSLI
Before 2018, investigators routinely obtained CSLI through a court order under the Stored Communications Act. That order required only “specific and articulable facts” showing the records were relevant to an investigation, a standard well below probable cause.1Office of the Law Revision Counsel. 18 USC 2703 – Required Disclosure of Customer Communications or Records The Supreme Court upended that practice in Carpenter v. United States, holding that people have a reasonable expectation of privacy in the record of their physical movements and that acquiring seven days of historical CSLI qualifies as a Fourth Amendment search.2Legal Information Institute. Carpenter v United States
After Carpenter, officers must present a judge with an affidavit establishing probable cause before compelling a carrier to hand over historical CSLI. The warrant has to specify the phone number or device identifier and the date range being sought. If the government skips this step, the evidence can be suppressed under the exclusionary rule.2Legal Information Institute. Carpenter v United States
The Court was careful to say it was deciding only that seven days of CSLI triggers Fourth Amendment protection. It explicitly declined to draw a bright line below which the government could freely access location records.3Justia Law. Carpenter v United States, 585 US (2018) That leaves a real gray zone for requests covering just a few days, and defense attorneys regularly argue that any period of CSLI tracking should require a warrant.
Exigent Circumstances and Emergency Disclosure
The warrant requirement is not absolute. The Carpenter Court acknowledged that exigent circumstances, such as pursuing a fleeing suspect, protecting someone facing imminent harm, or preventing destruction of evidence, can justify warrantless collection.4Supreme Court of the United States. Carpenter v United States, Opinion of the Court Lower courts had already approved warrantless access in bomb threats, active shootings, and child abductions, and the opinion left that practice intact.
A separate statutory channel sits in 18 U.S.C. § 2702, which permits a carrier to voluntarily disclose customer records to the government when the provider believes in good faith that an emergency involving danger of death or serious physical injury requires disclosure without delay.5Office of the Law Revision Counsel. 18 USC 2702 – Voluntary Disclosure of Customer Communications or Records Carriers keep around-the-clock law enforcement liaison teams. The officer submits an emergency disclosure form, and the carrier makes its own judgment about whether the situation qualifies. Agencies are expected to follow up with a court to justify the warrantless access after the emergency passes.
Good Faith for Pre-Carpenter Records
CSLI obtained before Carpenter under the older Stored Communications Act standard is not automatically thrown out. On remand in Carpenter’s own case, the Sixth Circuit held that the FBI agents who gathered his records had reasonably relied on the statute as it existed at the time, and the evidence survived under the good faith exception. The warrant rule governs collection going forward.
Real-Time Tracking and Cell Site Simulators
Real-time CSLI is a different animal from stored records. Instead of pulling historical logs, the carrier triggers the phone to check in with a tower right now, revealing the device’s current location. Because this amounts to live surveillance, courts generally require a warrant based on probable cause. The main exception is the same emergency pathway under § 2702.
A cell site simulator, sometimes called a Stingray, is a portable device that mimics a cell tower and tricks nearby phones into connecting to it, revealing their location and identifying information. Because simulators sweep up data from every phone in the area rather than just the target, their use raises serious Fourth Amendment concerns. The Department of Justice adopted a policy in 2015 requiring federal agents to obtain a search warrant before deploying one, except in cases involving exigent circumstances or situations where the law does not otherwise require a warrant and obtaining one is impractical.6Department of Justice. Department of Justice Policy Guidance – Use of Cell-Site Simulator Technology
Under DOJ policy, the warrant application must disclose that the device will cause both the target phone and nearby phones to transmit identifying data, and that non-target devices may experience temporary service disruption. Data from non-target phones must be deleted, and data from the target device must be purged once the phone is located.6Department of Justice. Department of Justice Policy Guidance – Use of Cell-Site Simulator Technology No federal appellate court has issued a definitive ruling on whether simulator use is itself a Fourth Amendment search, but the DOJ’s own warrant rule effectively concedes the point for federal investigations.
Geofence Warrants and Tower Dumps Are Not CSLI
Two adjacent tools often get confused with CSLI, and the rules differ.
A geofence warrant goes to a technology company rather than a wireless carrier. Investigators ask for a list of every device present in a defined geographic area during a specific time window, usually drawn from Google’s Location History database. The warrants typically ran in three steps: an anonymized device list, a narrowed subset based on behavioral patterns, and then identifying information for the remaining accounts.7Congressional Research Service. Geofence and Keyword Searches – Reverse Warrants and the Fourth Amendment In August 2024, the Fifth Circuit held that geofence warrants are categorically prohibited by the Fourth Amendment as modern general warrants.8United States Court of Appeals for the Fifth Circuit. United States v Smith Other courts have upheld them when the geographic area and time frame were narrowly drawn. The Supreme Court granted certiorari in Chatrie v. United States in January 2026 and heard argument in April 2026.
A tower dump, by contrast, is a request to a wireless carrier for records of every device that connected to a particular cell tower during a specified window. The Carpenter Court expressly declined to address tower dumps, and federal courts remain split. One district court found no reasonable expectation of privacy in five hours of tower-level CSLI, reasoning it fell far short of Carpenter‘s seven-day benchmark; another court reached the opposite conclusion for short-term tower dump data.7Congressional Research Service. Geofence and Keyword Searches – Reverse Warrants and the Fourth Amendment Until the Supreme Court or Congress resolves the question, legality depends on the jurisdiction.
How Long Carriers Keep CSLI
No federal law tells carriers how long they must keep CSLI. Each company sets its own schedule based on storage costs, network management, and regulatory expectations. Once the data is purged, it is gone. The general picture from the most recent public disclosures:
- AT&T retains device-specific location data for approximately 13 months, and historical call detail records that include cell site information for up to five years.
- Verizon keeps CSLI for about one year.
- T-Mobile stores location data for up to 24 months.
These timelines can change without public notice, and the type of record matters. A carrier may keep tower connection logs longer than GPS-derived location data, or the reverse. If location evidence matters to a case, act fast. A delay of even a few months can mean the records no longer exist.
Preservation Letters
Federal law gives investigators and attorneys a tool to prevent carriers from deleting relevant data while a warrant or subpoena is being prepared. Under 18 U.S.C. § 2703(f), a government entity can send a preservation request to a carrier, which then must retain all records for 90 days. The period extends for another 90 days if the government renews the request.1Office of the Law Revision Counsel. 18 USC 2703 – Required Disclosure of Customer Communications or Records Without a preservation letter, the carrier follows its normal deletion schedule, and no court order after the fact can bring back what has been scrubbed. On older cases, defense counsel should confirm early whether a preservation request was issued and when.
Challenging CSLI Evidence
CSLI is powerful evidence, but it is far from bulletproof. The biggest vulnerability is the gap between what the data actually shows and what the prosecution claims it shows. A tower connection log tells you which tower and sector handled a phone’s signal. It does not tell you the phone was at any single point on a map. Prosecution witnesses sometimes plot a device as a dot when the honest representation is a broad area spanning blocks or even miles. Terrain, buildings, weather, network congestion, and antenna settings all affect which tower a phone connects to, and a phone does not always connect to the nearest one. A device on the edge of two coverage areas might ping a tower a mile away while sitting next to a closer one that happens to be congested.
Defense experts attack these oversimplifications on several fronts:
- Coverage mapping. Prosecution models that assume a phone always connects to the nearest tower, sometimes called the “granulization theory,” have been rejected by courts. Reliable coverage analysis requires actual drive-test data or propagation modeling, not an analyst’s experience alone.
- Environmental interference. Steel, concrete, glass, hills, foliage, and water block or redirect radio signals. A prosecution exhibit showing neat circular coverage areas around a tower ignores how the real world scrambles those patterns.
- Proprietary location techniques. Some carriers use proprietary methods to estimate a device’s position and report a location with a “confidence level.” When the carrier refuses to disclose how that estimate was calculated, independent verification is impossible and reliability is open to attack.
- Admissibility standards. Courts applying Daubert or Frye can exclude CSLI analysis that relies on methods lacking scientific validation. If the analyst cannot explain the methodology connecting the raw data to the conclusion, the testimony may be kept out.
Suing Over Unauthorized Disclosure
When a carrier or government entity obtains or discloses CSLI in violation of federal law, the person whose data was exposed can sue under 18 U.S.C. § 2707. The statute guarantees a minimum recovery of $1,000 even when actual damages are difficult to prove, and allows courts to award actual damages plus any profits the violator gained from the disclosure.9Office of the Law Revision Counsel. 18 USC 2707 – Civil Action Punitive damages are available for intentional violations, and a successful plaintiff can recover attorney fees and litigation costs.
The statute of limitations is two years from when the victim discovered or reasonably should have discovered the violation. Carriers and officers who relied in good faith on a warrant, court order, grand jury subpoena, or statutory authorization have a complete defense.9Office of the Law Revision Counsel. 18 USC 2707 – Civil Action That defense is broad enough to cover most routine law enforcement requests, but it would not shield an officer who fabricated an emergency or a carrier that handed over records with no legal process at all.