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Mobile Phones: Phone Components and Sensors

This page was translated from English. The English version may be more up-to-date.

Phone Components and Sensors anchor link

The following section explains other physical components of smartphones that use various antennas built into the modern phone to communicate different types of environmental information to applications.

GPS anchor link

The Global Positioning System (GPS) lets devices anywhere in the world figure out their own locations quickly and accurately. GPS works based on analyzing signals from satellites that are operated by the U.S. government as a public service for everyone. It's a common misconception that these satellites somehow watch GPS users or know where the GPS users are. In fact, the GPS satellites only transmit signals; the satellites don't receive or observe anything from your phone, and the satellites and GPS system operators do not know where any particular user or device is located, or even how many people are using the system.

This is possible because the individual GPS receivers (like those inside smartphones) calculate their own positions by determining how long it took the radio signals from different satellites to arrive.

So, if GPS satellites aren’t tracking users, how is “GPS tracking” done? Usually, this tracking is done by apps running on a user’s smartphone. These apps ask the phone's operating system for its location (determined via GPS). In turn, with modern phone permissions, the user is asked if they would like to share their location before the app can use it. If permission is granted, then the apps are able to transmit this information to someone else over the Internet. There are also GPS-receiving devices like cars and smart home hubs that can transmit over a network as well. Multiband support is now available in modern phones for other government sponsored positioning systems such as GLONASS (RU), BDS (CN), and GALILEO (EU).

NFC (Near Field Communication) anchor link

This wireless, radio-frequency based identification system exists in modern phones. It is mainly marketed through contactless mobile payment technologies or contactless identification systems. The range of NFC normally maxes out at 4cm and can store around a few hundred bytes to few kilobytes of data at a time. NFC technology can also passively read RFID (radio-frequency identification) tags embedded in posters and other objects. This information is relevant, because even though this isn’t a technology that accurately knows where you are in the world, it can be logged when you use contactless payment or enter a building, placing you at a specific time and place. NFC technology in phones can also be set up to be used with other “smart home devices”, to turn them on or off. If you’re concerned about this capability , turn the NFC sensor in your phone off. In Android settings, this is normally under Settings > Connected Devices > Connection preferences. In iOS, NFC is limited to applications like Apple Pay, so there is no universal way to turn this off. However, its use is very limited on iOS.

Biometric Sensors anchor link

These consist of fingerprint sensors or a facial recognition system to help you log into your phone. These are considered more secure from purely a phone safety aspect, but are not necessarily considered safer in various situations with law enforcement.

Motion Sensors anchor link

There are other phone sensors that don’t necessarily provide as much information as cell towers, GPS, or WiFi. The following are listed to build on the knowledge of what exists inside your smartphone, as applications often read sensor information that can potentially identify your device, even though the potential to be detected with these methods is minimal.

Accelerometer: A motion sensor, often used in fitness applications to log what type of activity the user is doing. This is also used in many navigation applications that measure the rate of speed you are travelling. This sensor has been flagged in security research as being able to detect the vibrations of and identify different keystrokes on a nearby computer with 80% accuracy. This is hard to detect by normal means, but putting your phone in your bag or pocket can mitigate this concern.

Gyroscope: A motion sensor that detects orientation and angular velocity. This sensor is constantly sensing new information since we are always moving our phone’s position. This sensor has been noted in previous research as acting as a potential crude microphone, due to their capability to pick up sound waves. There are other sensors that are environmental, motion, and position based that can measure room temperature, humidity, amount of light, Earth’s magnetic field, air pressure, etc. These sensors are normally very low powered and not as useful as the methods used by Location Tracking services to locate someone. The usage model for this sensor varies from iOS to Android (more strict on iOS because developers have to define the reason they are using this sensor). Generally, applications don’t need to ask for permission to use these sensors. However, it takes an active amount of targeting and resources to use these sensors in a way that can compromise a user.

Other sensors to be aware of:

  • Magnetometer
  • Barometer
  • Proximity sensor
  • Ambient light sensor
  • Soli sensor (Proprietary to Pixel 4 phones)
  • LiDAR
  • U1 chip (Antenna proprietary to iPhone)