A quick and dirty guide to monitoring mobile phones during protests

As riots against police brutality and institutionalized racism swept across the country, many people were exposed to the full power of law enforcement weapons and surveillance for the first time. Whenever protesters, cell phones and police are in the same place, protesters should pay attention to cell phone surveillance. Usually, security practitioners or other protesters respond to this issue through suggestions provided by local law enforcement agencies using cell location simulators (also known as CSS, IMSI catchers, stingrays, earth boxes, hail, fake base stations, or crosses). However, in many cases, this suggestion is wrong, or it is due to fundamental reasons such as not knowing what the cellular base station simulator is, its function and frequency of use.

Denial of service or signal interference is an additional function of CSS. In fact, the FBI has admitted that CSS can cause signal jammer to local personnel. Unfortunately, for the same reasons, it is difficult to determine the use of CSS, and it is difficult to tell how often they interrupt service, whether intentionally or unintentionally. Signal towers that look like signal interference may also be overloaded and disconnected. If many people suddenly gather in one place, it may overload the network, which is not the purpose of the design.

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How to protect yourself from cellular signals

As we mentioned in our self-defense guide for monitoring protesters, the best way to protect yourself from cellular site simulators is to put your phone in airplane mode and then turn off GPS [2], WiFi and Bluetooth, and cellular data. (Although “receive only” GPS and not lose its own location information, many apps track GPS location data, which is ultimately stored in a database that law enforcement agencies can search for later.)

We know that some IMSI capturers can also intercept content, but as far as we know, if you don’t downgrade your cellular connection to 2G, none of them can do it. If you want to protect your device from this attack, the best option is to use encrypted messages such as Signal or WhatsApp and put it in airplane mode when you find that your phone has fallen to 2G. (There are many valid reasons. Your phone may downgrade some of your connections to 2G, but it is safer than regretting.) However, an important part of the protest may be live broadcast/recording and immediate upload of police reports against protesters. Violent video. This is inconsistent with the recommendation to keep the phone off/in airplane mode. Up to you

Unfortunately, iOS and Android currently do not provide an easy way to force your phone to use 4G only, although developers can of course add it to their operating systems. If you can turn off 2G on your phone, this is a good preventive measure.

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