Mobile phone tracking is a process for identifying the location of a mobile phone, whether stationary or moving. Localization may be effected by a number of technologies, such as themultilateration of radio signals between (several)cell towers of thenetwork and the phone or by simply usingGPS tracking. To locate a mobile phone using multilateration of mobile radio signals, the phone must emit at least the idle signal to contact nearby antenna towers and does not require an active call. TheGlobal System for Mobile Communications (GSM) is based on the phone'ssignal strength to nearby antenna masts.^[1]

Mobile positioning may be used forlocation-based services that disclose the actual coordinates of a mobile phone.Telecommunication companies use this toapproximate the location of a mobile phone, and thereby also its user.^[2]

The location of a mobile phone can be determined using several complementary technologies. Modern phones typically use aHybrid positioning system that combines these methods to provide the fastest and most accurate location possible.

This is the most common method, where the device itself calculates its own position.

• GNSS /GPS: The phone uses a built-in receiver to calculate its precise location from signals broadcast bysatellite navigation constellations (like GPS,GLONASS, orGalileo). This is the most accurate method when outdoors.
• Wi-Fi Positioning: In areas with poor satellite reception, such as indoors or in dense "urban canyons," the phone can scan for nearbyWi-Fi networks. It then calculates its position by cross-referencing the unique identifiers (BSSIDs) of these networks against a global, crowdsourced database of their locations.^[3]
• Fingerprinting: This technique records the "signature" of home and neighboring cell signal strengths at different points in an area. The device can then match its current signal signature to this database to determine its location.^[4]

This method relies on the cellular network infrastructure to determine the phone's location. The advantage is that it can be implemented non-intrusively by the service provider without any special software on the handset.^[5]

• Cell ID: The least accurate method, which uses the known location of the singlecell tower the phone is communicating with. Its precision is low, especially in rural areas where cell towers are far apart.
• Multilateration: More advanced systems use the signal strength and timing from multiple adjacent cell towers to triangulate the phone's position. This is more accurate in urban areas where cell tower density is high.^[6]

For anylocation-based service to function, the position data calculated by the phone (whether from GPS, Wi-Fi, or the network) must be transmitted to a server. The phone's built-in cellular modem sends thistelemetry data over the mobile network (e.g., 4G/5G).

This "phone-as-a-sensor" model is the foundation for many modern on-demand services and is a key part offleet digitalization. Applications for food delivery, courier services, and ride-hailing (likeUber orLyft) rely on the phone's transmitted location data to function. The phone itself acts as theGPS tracking unit for the service'sfleet management platform, allowing it to dispatch the nearest driver, provide customers with a real-timetrack and trace map, and calculate billing. The reliability of these services depends on this constant data connection; for example, theshutdown of older 3G networks required many commercial services to ensure their devices were 4G or 5G capable to maintain connectivity.^[7]

In order to route calls to a phone,cell towers listen for a signal sent from the phone and negotiate which tower is best able to communicate with the phone. As the phone changes location, the antenna towers monitor the signal, and the phone is "roamed" to an adjacent tower as appropriate. By comparing the relative signal strength from multiple antenna towers, a general location of a phone can be roughly determined. Other means make use of the antenna pattern, which supports angular determination andphase discrimination.

Newer phones may also allow the tracking of the phone even when turned on but not active in a telephone call. This results from the roaming procedures that perform hand-over of the phone from one base station to another.^[8]

A phone's location can be shared with friends and family, posted to a public website, recorded locally, or shared with other users of a smartphone app. The inclusion of GPS receivers on smartphones has made geographical apps nearly ubiquitous on these devices. Specific applications include:

• Geo-fence specific locations of interest such as No Fly Zones
• GPS navigation and maps
• Locator apps likeFind My Friends
• Dating apps likeGrindr
• Recording a journey, for example to show ahiking accomplishment
• Forquantified self purposes such as fitness tracking
• GPS drawing

In January 2019, the location of her iPhone as determined by her sister helped Boston police find kidnapping victim Olivia Ambrose.^[9]

Locating or positioning touches upon delicateprivacy issues, since it enables someone to check where a person is without the person's consent.^[10] Strict ethics and security measures are strongly recommended for services that employ positioning.

In 2012Malte Spitz held aTED talk^[11] on the issue of mobile phone privacy in which he showcased his own stored data that he received fromDeutsche Telekom after suing the company. He described the data, which consists of 35,830 lines of data collected during the span ofGermany'sdata retention at the time, saying, "This is six months of my life [...] You can see where I am, when I sleep at night, what I'm doing." He partnered up withZEIT Online and made his information publicly available in aninteractive map which allows users to watch his entire movements during that time in fast-forward. Spitz concluded that technology consumers are the key to challenging privacy norms in today's society who "have to fight for self determination in the digital age."^[12][13]

TheChinese government has proposed using this technology to track commuting patterns ofBeijing city residents.^[14] Aggregate presence of mobile phone users could be tracked in a privacy-preserving fashion.^[15] This location data was used to locate protesters duringprotests in Beijing in 2022.^[16]

InEurope most countries have a constitutional guarantee on thesecrecy of correspondence, and location data obtained from mobile phone networks is usually given the same protection as the communication itself.^{[17][18][19][20]}

In theUnited States, there is a limited constitutional guarantee on theprivacy of telecommunications through theFourth Amendment.^{[21][22][23][24][25]} The use of location data is further limited bystatutory,^[26]administrative,^[27] andcase law.^[21][28] Police access of seven days of a citizen's location data is unquestionably enough to be afourth amendment search requiring bothprobable cause and awarrant.^[21][29]

In November 2017, theUnited States Supreme Court ruled inCarpenter v. United States that the government violates the Fourth Amendment by accessing historical records containing the physical locations of cellphones without a search warrant.^[30]

• Varshavsky, Alex; Chen, Mikey; Froehlich, Jon; Haehnel, Dirk; Hightower, Jeffrey; Lamarca, Anthony; Potter, Fred; Sohn, Timothy; Tang, Karen; Smith, Ian."Are GSM phones THE solution for localization?"(PDF).In 7th IEEE Workshop on Mobile Computing Systems and Applications (HotMobile). IEEE Computer Society:20–28.
• Dan Goodin (17 February 2012)."Location tracking of GSM cellphones: now easier (and cheaper) than ever".Arstechnica. Conde Nast.

• GSM standard
• Mobile technology
• Crime prevention
• Criminal investigation
• Espionage techniques
• Mobile telecommunication services
• Privacy
• Geopositioning
• Tracking

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