Input: How Do Mobile Devices Work?

Credits Alix Dunn Last Updated 2014-03

The content you choose for this section will vary based on your participants, their devices (feature phone vs smartphone), their interest or concern with the topic, and time. Mobile alone could constitute a typical multi-day training, however what's provided here is a summary of the fundamentals of mobile devices and mobile networks.

ADIDS Element


Parent Topic(s)

How Mobile Networks Work


45-70 minutes

Materials to Prepare

  • Whiteboard or flipchart and markers
  • Projector for videos or images (which should also be prepared before the session)
  • Any physical examples of a mobile device that you can offer (either your own mobile phone, or separate pieces of a phone or other type of mobile device)


Mobile data dongle, that can be used to demonstrate the SIM and IMEI of the hardware.

Input Session

These are detailed notes for leading a brief introduction or discussion about the components of a mobile phone. The number of components you choose mention will depend on your time available and the enthusiasm of your participants to share and point out various components.

Trainer’s Note

If your only mobile session is focused on a specific functionality, tool, or app that participants access via mobiles, you may also want to pull input content from other topics (such as Safer Browsing - HTTPS and SSL or Data Backup Basics to combine with this core Input about mobile fundamentals.

We recommend that you at least mention the antenna, battery, SIM, baseband, and removable media, and cameras (if present). If there are any particular components you want to focus on based on trainee concern or expressed need, build in time for these as well; for example, if you are training for video collection and uploading, you’ll need to discuss cameras, microphones, and removable media like SD cards.

Step 1. What’s a Phone Made Of?

Phones are remarkably complex devices.

There are also many other devices enabled to work on mobile networks as well that may not be phones, such as tablets and USB dongles for accessing mobile data on a computer. Although some phones, particularly smartphones, have much more advanced capabilities, all phones share several core components:


Antennas, which permit communication between a mobile device and external networks, may be visible on older devices - some significantly older models requiring them to be pulled out manually for use. Most newer phones have the antennas built directly into its body, so they are no longer “visible.” Aside from the antenna responsible for communicating with the mobile network, there may also be antennas for WiFi; some manufacturers combine these functions into one antenna for the entire device.


A battery is what stores energy in order to power a mobile device; in most phones, batteries are easy to remove. In some newer smartphones (notably iPhones and later Samsung Galaxy S models), batteries are not designed for removal and can be hard to access.Removable batteries are preferable for users who use tactics to increase their security.

Baseband Microprocessor

This component manages the communications of the phone, including the communications and commands from the user to the phone, and from the phone to and from the mobile network. The baseband of a phone is usually considered highly “proprietary” by manufacturers and can be considered a “black box” (inaccessible and not easily tampered with) in terms of its communication protocols, how they are controlled, and other network/device-specific functions.

The capability of mobile networks to be able to turn on a phone, identify its location, listen via it’s microphone, and download data from the device is tied to the baseband on a device - this is called the “E-911” capability. Many countries require that mobile devices have this capability built in since September 11th; therefore, almost all mobile devices can be “enabled” this way without the authorization of the user via mobile networks. The only way to prevent this as the owner of a device is to completely remove the battery. This is why the “black box” proprietary nature of basebands is an important characteristic of contemporary mobile devices.

SIM and SIM Slot

This is where the SIM card is stored in a mobile device. There is a limited capacity for data storage on your SIM card, and some users can decide whether or not they want to save certain data to their SIM, internal phone memory, or to removable media. Mention that some phones are designed to manage multiple SIM cards; other phones operating on non-GSM networks (usually CDMA) do not have any SIM cards.

Removable Media

Removable media are any kind of external memory storage that can be inserted into and removed from a mobile device; these are usually SD-cards and micro-SD cards. Some phones also have Infrared (IR) ports for “beaming” data from one phone to another, as well as Bluetooth functionality.


Most phones now have cameras that can take pictures and/or video, in particular smartphones. Many also feature cameras mounted to both the back and front of the device, frequently for use in tandem with video chat applications such as Facebook Messenger or Skype.

Circuit Board and Chips

What this consists of and looks like will vary depending on the phone. There are chips for translating analog/digital signals, read-only memory (ROM), flash memory chips that store data and the phone’s operating system, microprocessors to process data (such as data sent via Bluetooth), and components that manage the power and charging capabilities of the phone.


Screens will range in size and type; some will be monochromatic (black on a single color background), while others can display a wide range of colors at high resolutions. Most older, monochromatic screen displays are LCD (liquid crystal display), but there is now a wider variety of screen types as phones are able to display more graphics and colors (such as 4D and AMOLED), with touchscreens commonplace on nearly all smartphones.


Found predominantly on feature phones, keypads can range from the limited, twelve-button numerical layout common on early handsets, to a full keyboard for some earlier smartphones and Blackberries. More common now on smartphones is an integrated keypad on-screen, also known as a ‘soft keyboard,’ from its use of software to display and receive input.


Port are the insertion points on a mobile device for different data transfer, power-charging, or audio-visual peripherals. The most common are headphone jacks and mini/micro-USB ports, found along the top and bottom sides of a device.

Microphone & Speaker(s)

Microphones are acoustic-to-electronic input recorders, that translate sounds into data, typically for transmission over the network (voice calls over Data, WiFi, or GSM/CDMA). Microphones on mobile phones are primarily for capturing voice for use in calling, but may also be used to record audio for documentation or other purposes. Speakers are audio output points on a mobile device, typically for the playback of sound data received by your device (e.g. when you receive and answer a phone call).

Step 2. Your Identity on the Mobile Network

In order to function on the mobile network, and properly relay information to and from your device to those of others or across the internet, mobile phones create and rely upon different identification mechanisms and information. Below are some of these data types, the technology they rely upon or interact with, and how they can potentially identify you:

IMEI Number

The International Mobile Equipment Identity number, which uniquely identifies the hardware of your mobile device - this is usually a handset, but can also include other mobile devices, such as a wireless modem.

IMSI Number

The International Mobile Subscriber Identity number, which uniquely identifies the SIM card in a mobile device. This is tied to a user’s account and phone number.

Registered SIM

A SIM card is what your phone uses to register with a given mobile network, and then make that network’s services available to a device. A registered SIM requires users to provide identification for activation; this could include fingerprints and photos, or proof of address. All contract SIMs are effectively registered SIMs, because the mobile network operator has a record of your identity, billing address, and more.

Unregistered SIM

In some countries, registration with personal identification is not required to purchase a pay-as-you-go SIM; in others, unregistered SIMs are sold on the black market. Recognize that SIMs given to you by another person (colleague, family member, acquaintance, or stranger) may still be registered, just not to you. They could, depending on the degree of separation between you and the person giving you the SIM, be tied back to you via human networks, or by your behavior with the device if they know your typical “patterns of use.”

TMSI Number

The Temporary Mobile Subscriber Identity number, a temporary number that is re-assigned regularly according to location or coverage to help manage roaming and other services. (Primarily relevant for mobile network management.)

Step 3. What the Mobile Network Sees

Now, switching perspectives from the user to the network, this step provides an overview of what a mobile network “sees” via the technology and identifying information described above that is regularly provided by a mobile device.

Network Cell

A network cell is a defined geographic area that can cover any area from a few meters to several kilometers - mobile networks can see the network cell in which a phone is located. Cells are generally larger in rural areas, smaller in urban areas, and even very small cells in buildings that use a repeaters to improve service signals in the immediate area.


The location of the subscriber within a cell is also visible to the mobile network. This is determined by triangulating the signal from a device according to the location(s) of nearby towers. Again, location accuracy depends on the size of the cell - the more towers in the area, the more accurate the positioning.

Usage Data (or Metadata)

The mobile network operator logs and records the metadata around your content. This includes all calls (both ingoing and outgoing), sending and receiving of SMS and MMS messages, mobile data usage, as well as the exact time and approximate location of each of these. All of these pieces of data can identify users individually, or in aggregate with others. Even accessing data using encryption (e.g., using HTTPS to access a website), which cannot be “seen” at the mobile network operator level, is tagged with the time and location where you accessed it, even if the content is not known.


The logging (or recording) of the type, length, location, and times of service usage such as calling, texting, or web browsing is tagged with uniquely identifying information. This is all tied to the record that a mobile network operator has associated with an individual registration, which is the information provided when accessing services (such as buying a SIM or a handset).

The length of time that operators store these logs can vary from country to country, depending on the legal requirements by the government. They can also vary between operators in a single country, as some will keep logs for the legally minimum length of time, while others may choose to keep them longer than they are legally required to.


Show participants Die Zeit’s visualization of Malte Spitze’s mobile data use over six months, which he requested from his mobile network operator. Describe what the visualization is showing so participants can follow along, including connecting with network cells as he physically moves around, and the icons denoting calls, SMS, and data usage.


The mobile network operator (and/or relevant law enforcement agencies through operators or by using devices called “IMSI Catchers”) is technically capable of intercepting and recording calls, as well as recording all information sent and received via SMS and MMS, both of which cross the network in the clear as ‘plaintext’. Operators and/or law enforcement are also technically capable of ‘inspecting’ unencrypted data usage, including the content of search engine queries, unencrypted logins to various services, and browsing behavior.

This content data can be cross-referenced against usage and user metadata, to provide a comprehensive picture of the frequency, scope, and patterns of of your mobile use. In addition, our behavior can “fingerprint” us as unique, even if an operator doesn’t have any identifying information about us.


Show participants Unique in the Crowd: The Privacy Bounds of Human Mobility, a 2012 study of 1.5 million mobile users over 15 months. This study found that with hourly samples taken of our location and usage, 95% of users can be uniquely distinguished using only four data points of usage. This means that our behavior unique identifies us, even if our identity is not tied to the device and its identifying information on a mobile network.

Step 5. Additional Content for Smartphone Users

Since smartphones offer even more functionality and options than feature phones, the amount of information that can be observed and logged is far greater. In addition, smartphone users are sharing that very detailed identifying information about themselves and their usage to far more companies than just their mobile network operator - every app you choose to install can also send selected data about your usage, call times, contacts, and data use to whomever makes that app.

What an app can see and log is often set by the app designer, but there are very few laws and regulations constraining what they can design their app for. Similarly, the operating system and manufacturer of a smartphone has implications on where your data goes and who can see it aside from your mobile network operator.

Android vs. iPhone: Similarities and Differences

Operating Systems

Android devices share a massive amount of user data with Google, since their operating system is deeply entwined with a user’s Google account. If you use Google services and apps as well as an Android-powered smartphone, Google knows an overwhelming amount of information about you – possibly more than you’d realize about yourself, since they log and analyze that data.

Similarly, iPhones (using iOS as their operating system) provide a similar amount of information about users to Apple, which can be combined with a user’s data if they use other Apple products and services. In addition, iPhone and Apple are highly proprietary and their software and hardware are closed source. This includes the iPhone itself, as well as the Apple apps that run on it; in comparison, Android is open source, which allows everyone to review their code and know what the Android does.

App Stores

Android is designed to download apps from the Google Play Store, which gives users a generic list of the type(s) of access any third-party app from the Play Store can their app is installed on your device, ranging from everything you do to almost nothing.

In the iPhone App Store, this is not the case - users do not know what third-party apps can access on their iPhone, with no level of detail provided to users upon app download. In addition, the full-disk encryption on iPhones is designed to work for all built-in Apple iPhone apps, but may not work for third-party apps.

The designers of third-party apps can design their apps to work with the iPhone’s built-in disk encryption (also called “data protection”); however, because of this, it is not clear what kind of access third-party apps have to usage data from their phones. Furthermore, nor do users know if the data associated with third-party apps is encrypted on their iPhone, which potentially makes it easier to access physically on the device.

Location Information

Smartphones are able to use GPS (Global Positioning System) satellites in addition to the approximate location triangulation of mobile network towers can provide. This gives far more detailed location data to operators and to any apps who have access to that information. This more precise location can be attached, along with the date and other information, to any pieces of data that the phone collects to post online or store on its memory.