Cellular triangulation is the technique wireless networks use to estimate a phone’s location by measuring its signal against three or more cell towers. After the Supreme Court’s 2018 decision in Carpenter v. United States, law enforcement generally needs a warrant supported by probable cause before it can obtain that location data from your carrier. The technique itself runs constantly in the background of every connected phone, which is why the legal rules around access matter as much as the engineering behind it.
How the Technique Works
Your phone talks to nearby towers even when you are not using it. The device scans for signals, connects to a primary tower, and stays aware of several others in range. Each tower is divided into sectors covering a wedge-shaped area, so the network already knows the rough direction of your phone relative to a given antenna.
Distance is estimated using Received Signal Strength Indication, essentially a measure of how loud the tower’s signal sounds to your phone. A stronger signal means you are closer. Once the network has readings from at least three towers, it draws overlapping circles around each one, with the radius representing estimated distance. The area where those circles intersect is your approximate location. More advanced versions also measure how long the signal takes to travel between the device and each tower, which tightens the estimate.
This works independently of GPS. A phone with no satellite fix, a dead GPS chip, or location services turned off still communicates with towers and still generates the signal data that makes triangulation possible. That is why carriers hold location records on virtually every connected phone by default.
How Accurate Is Cellular Triangulation
Accuracy depends heavily on the generation of wireless technology and the physical environment. Fourth-generation LTE triangulation typically produces estimates within a few hundred meters. 5G New Radio is substantially tighter because it supports up to 100 MHz of bandwidth in lower frequency bands and 400 MHz in millimeter-wave bands, compared to LTE’s 20 MHz ceiling. Wider bandwidth lets the network measure signal travel times with finer resolution, and the timing error shrinks proportionally to the square of the bandwidth increase.
5G also adds angle-based positioning. Massive antenna arrays use beamforming to steer signals toward individual devices, and the system measures both the angle of departure from the tower and the angle of arrival from the phone. Combined with timing data, this can locate a device in a dense urban 5G area with accuracy in the single-digit meters, precise enough to place someone in a specific room rather than a general neighborhood.
Physical conditions push the numbers the other way. Tower density is the biggest variable. In cities, towers sit close together, producing tighter estimates. In rural areas, towers may be miles apart and a phone may reach only one or two, which breaks the geometry triangulation depends on. Large buildings, mountains, and heavy tree cover cause multipath interference, where a signal bounces off a surface before reaching a tower and arrives later than it should, tricking the system into calculating the wrong distance. Rain and snow absorb radio energy and weaken connections.
Indoors is the hardest case. Construction materials absorb signal energy and add propagation delays that translate directly into distance errors. A phone deep inside a concrete office building can produce a location estimate hundreds of meters off, even in a city with dense tower coverage.
Who Can Access Your Location Data
The Fourth Amendment protects against unreasonable searches and seizures, and the Supreme Court has extended that protection to the location records your phone generates. In Carpenter v. United States, the Court held that individuals maintain a legitimate expectation of privacy in their physical movements as captured through cell-site location information (CSLI), and that the government must generally obtain a warrant supported by probable cause before acquiring those records.1Justia. Carpenter v. United States, 585 U.S. 377 (2018)
The Court held that accessing seven days of CSLI is a Fourth Amendment search, but declined to draw a bright line for shorter periods. The majority wrote that it was “sufficient for our purposes today” to address seven days and did not decide whether a limited amount of historical CSLI might be obtained without a warrant.1Justia. Carpenter v. United States, 585 U.S. 377 (2018) Most lower courts have since applied the warrant requirement to shorter periods, though the question is not fully settled.
The Statutory Framework
The statute governing what carriers can be forced to disclose is the Stored Communications Act, Title II of the Electronic Communications Privacy Act, at 18 U.S.C. §§ 2701–2712.2Bureau of Justice Assistance. Electronic Communications Privacy Act of 1986 Section 2703 requires a warrant for stored content. For non-content records, a court order under § 2703(d) may be enough if the government offers “specific and articulable facts showing that there are reasonable grounds to believe” the records are relevant and material to an ongoing criminal investigation.3Office of the Law Revision Counsel. 18 US Code 2703 – Required Disclosure of Customer Communications or Records
After Carpenter, comprehensive CSLI requires a full warrant regardless of what the statute alone would allow. The § 2703(d) order still applies to less sensitive categories of records, but location tracking has been elevated to warrant-only territory by constitutional mandate.
Real-Time Tracking and Pinging
The rules above mostly address historical CSLI, meaning records of where a phone has already been. Real-time surveillance raises separate issues. Agencies sometimes ask a carrier to ping a phone, forcing it to communicate with nearby towers and reveal its current location. The statutory tool often used is a pen register or trap-and-trace order under 18 U.S.C. § 3122, which requires only that a government attorney certify that “the information likely to be obtained is relevant to an ongoing criminal investigation.”4Office of the Law Revision Counsel. 18 USC 3122 – Application for an Order for a Pen Register or a Trap and Trace Device That standard is lower than probable cause. Whether it is constitutionally adequate for real-time location tracking after Carpenter is an open question the Supreme Court explicitly declined to answer.
Cell-Site Simulators
Law enforcement also uses cell-site simulators, sometimes called Stingrays or IMSI catchers, which mimic legitimate towers and trick nearby phones into connecting. Once a phone connects, the simulator captures identifying information and location data. The Department of Justice announced in 2015 that federal agents must obtain a warrant supported by probable cause before using one. State and local agencies follow a patchwork of rules. Some states require a warrant, others allow use under the pen register standard, and some have no specific authorization requirement.
Emergencies
The Carpenter Court carved out a clear exception for exigent circumstances. Its opinion states that “case-specific exceptions may support a warrantless search of an individual’s cell-site records” when “the exigencies of the situation make the needs of law enforcement so compelling that a warrantless search is objectively reasonable.” The Court identified three categories: pursuing a fleeing suspect, protecting people threatened with imminent harm, and preventing the imminent destruction of evidence.5Supreme Court of the United States. Carpenter v. United States, 585 US 377 (2018) – Opinion The Court noted that lower courts have approved warrantless CSLI access for bomb threats, active shootings, and child abductions. The exception is fact-specific, and an agency that invokes it after the emergency has passed risks having the evidence suppressed.
Geofence Warrants Are a Different Animal
Cellular triangulation asks where a specific phone was. A geofence warrant asks which phones were near a specific location during a specific time window. The warrant usually targets a company like Google rather than a carrier, requesting anonymized data on every device in a defined area and then narrowing to identify suspects. Courts have split on whether these warrants satisfy the Fourth Amendment. The Fifth Circuit held in United States v. Smith that a geofence warrant amounted to a prohibited general warrant. A district court in United States v. Chatrie reached a similar constitutional conclusion but denied suppression under the good-faith exception, and the en banc Fourth Circuit affirmed that denial without resolving the constitutional question.6Congress.gov. Geofence Warrants and the Fourth Amendment
The Data Broker Workaround
The warrant requirement has a practical gap. Some agencies buy location data from commercial brokers instead of compelling it from carriers. Brokers aggregate location information from mobile apps, advertising exchanges, and software development kits embedded in everyday applications. Because the data is commercially available, agencies have argued that purchasing it is not a search subject to Fourth Amendment protections.
FBI Director Kash Patel confirmed during a March 2026 Senate hearing that the FBI purchases “commercially available information” to track people’s movement and location history, saying the practice is “consistent with the Constitution and the laws under the Electronic Communications Privacy Act.” Congress attempted to close the gap with the Fourth Amendment Is Not For Sale Act, which passed the House in April 2024 and would have prohibited law enforcement and intelligence agencies from purchasing location records from third parties.7Congress.gov. Fourth Amendment Is Not For Sale Act – HR 4639, 118th Congress (2023-2024) The bill did not become law.
The Federal Trade Commission has moved on the consumer protection side. In December 2024, the FTC took action against data aggregator Mobilewalla for collecting and selling sensitive location data tied to health clinics, religious organizations, correctional facilities, and political gatherings. The settlement order prohibits selling location data associated with sensitive locations and requires deletion of historical data.8Federal Trade Commission. FTC Takes Action Against Mobilewalla for Collecting and Selling Sensitive Location Data In January 2026, the FTC finalized a separate order against General Motors and OnStar for collecting and selling geolocation data without informed consumer consent.9Federal Trade Commission. Privacy and Security Enforcement These actions target corporate behavior, not government purchasing.
What Your Carrier Itself Can Do With the Data
Under 47 U.S.C. § 222, a telecommunications carrier may only use individually identifiable customer information in the course of providing the service the data was derived from, except as required by law or with the customer’s approval.10Office of the Law Revision Counsel. 47 USC 222 – Privacy of Customer Information For location data specifically, the statute requires “express prior authorization” before a carrier can treat you as having approved its use or disclosure. Buried terms-of-service language is not supposed to qualify.
The statute allows carriers to share location data with public safety answering points, emergency medical services, law enforcement, or hospital emergency departments when responding to a 911 call, and to inform a user’s legal guardian or immediate family in situations involving risk of death or serious physical harm. These exceptions are narrow and do not authorize general sharing with data brokers or advertisers.
What Happens When the Rules Are Broken
Location data obtained without proper authorization can be suppressed under the exclusionary rule, meaning prosecutors cannot use it at trial. Carpenter itself resulted in suppression of months of CSLI obtained under the older § 2703(d) standard. Courts recognize a good-faith exception where officers reasonably relied on existing law at the time, but that exception has narrowed as the warrant requirement has become well established.
Individuals whose data is accessed in violation of the Stored Communications Act can also sue under 18 U.S.C. § 2707. The statute provides for actual damages plus any profits the violator earned, with a floor of $1,000 in minimum damages. Willful violations can trigger punitive damages, and reasonable attorney’s fees are recoverable. A complete defense exists for anyone who acted in good-faith reliance on a court warrant or order. The statute of limitations is two years from when the victim discovered or reasonably should have discovered the violation.11Office of the Law Revision Counsel. 18 US Code 2707 – Civil Action
The E911 Exception
The FCC’s Enhanced 911 rules require wireless carriers to deliver a caller’s location to emergency dispatchers when a 911 call is placed, and this framework operates outside the warrant requirements that apply to criminal investigations. Under Phase I, carriers provide the phone number and the location of the cell site handling the call. Under Phase II, they must provide latitude and longitude, meeting accuracy standards generally within 50 to 300 meters depending on the technology.12Federal Communications Commission. Enhanced 911 – Wireless Services
Rules adopted in 2015 require carriers to provide either a dispatchable location (a validated street address) or coordinate-based location within 50 meters for 80 percent of wireless 911 calls.13Federal Register. Wireless E911 Location Accuracy Requirements For multi-story buildings, carriers that deploy vertical (z-axis) technology must locate callers within 3 meters above or below the device for 80 percent of 911 calls from z-axis capable phones, delivered as Height Above Ellipsoid and, where available, floor-level information.14Federal Communications Commission. Indoor Location Accuracy Timeline and Live Call Data Reporting Template This is the one context in which federal law mandates accurate location delivery rather than restricting access to it.