Federal Agents from the US Department of Homeland Security and the Justice Department used “a sophisticated cell phone cloning attack — the details of which remain classified — to intercept protesters’ phone communications” in Portland this summer, Ken Klippenstein reported this week in The Nation.
Some interesting tips in the article below that are just as valid for protesters in other countries protesting for democratic or constitutional rights. I so often also hear the excuse that "none of my friends use Signal" and really if you don't install it yourself, YOU are the one holding your friends back. Today's modern mobile phone really are capable of easily running many more instant messenger apps and services. There really is no excuse not to install a few alternative messaging apps.
See One Way to Prevent Police From Surveilling Your Phone
Use Signal and add a PIN code to your phone’s SIM card to help protect against spying.