Most people aren't aware that this kind of technology has been used on a regular basis for years by law enforcement in the US and in Canada .... especially in large gatherings or protest events.
https://en.wikipedia.org/wiki/Stingray_phone_tracker
Police set it up at major events to monitor public activity, track people and identify people .... most of the time as an excuse to monitor possible terrorist activity but worst to identify leaders and key people and figure out how to manage the protest event.
And sure, there are many opportunities to use encrypted devices and transmissions but those setups are only used by those who are organized enough and have setup those system ahead of time and know what they are doing. Most people are technically illiterate and still do a lot of communicating on open networks and systems that are easy to track and intercept.
Police go after low hanging fruit and once they find those people ... they go after them, arrest them to justify their continued use of this technology and to fund, develop and use even more invasive types of monitoring and scanning.
Which means that if you are attending any public protest event that will have hundreds or thousands of people in it ... never bring your personal every day phone. If you do, learn about encrypted communications and encrypting your device. It's best to just leave it at home and go without one or use a burner phone. Because if you are ever arrested with your phone, even if it is encrypted, you may be forced or coerced to unlock it. Most of us are not trained undercover agents that can face some officer pointing a gun at you or handcuffing you while shouting at you to unlock your phone.