Always try to speak with your source about classified information in person, as phone conversations can easily be intercepted by a third party. Popular services like Skype do not guarantee end-to-end encryption. Tools like Wire or Signal encrypt phone calls between devices, but not with a 100 percent guarantee.
Once you have arranged a place to meet your source, leave your phone at home or shut it off and take out the battery to ensure the device is offline. Additionally, you can use a Faraday Cage Phone Case which blocks electromagnetic signals. The ‘Edward Snowden method’ — named after the Wikileaks whistleblower — is to put the device in a refrigerator to guarantee privacy of a conversation.
You may also wish to limit the apps on your phone. Each time you install an app, it asks for access to specific functions, data or information on your device, leaving it open to vulnerabilities from outside sources. Just look at the Cambridge Analytica scandal to see how a seemingly innocuous app gleaned millions of people information to be wielded in a way these people did not agree to. If you must have the app, restrict their permissions on your devices’ settings. But bear in mind that the app will not work without these permissions.
Many additional links to explanatory videos can be found on investigative-manual.org
The goal of this chapter was to underscore the importance of a secure working environment and to make clear that there will never be a 100 percent security during an investigation. The next chapters will guide you on how to shape your investigation, ask your source the right questions and which interviewing techniques are best for obtaining the information you need.