As the vast majority of you know, governments are no strangers to using quasi-legal surviellance techniques to monitor the masses. They come in many forms, video surveillance, government-sponsored computer spyware, using hardware at the ISP's to directly intercept your internet traffic, and so on. What a lot of people don't know is most governments and even local law enforcement use a technology called "Cell site simulators". What this does, is it creates a fake cell phone site, that your phone or device will automatically connect to (they will always connect to the strongest cell site), and the person operating the site simulator can gather your IMSI (International Mobile Subscriber Identity), which is unique to every single cellular device, and use it to precisely track your individual phone. Even more disturbing is depending on who the user is, and their motives or intentions, they can remotely activate your microphone, your camera, listen in real-time to your phone conversations, read your text messages, install spyware remotely to your device, and many other malicious things.
Now the real kicker is, people like you and me can even do this very thing. All you need is a $20 USB software defined radio dongle, a laptop running Kali Linux, various GSM-LTE spying software for linux, and the time and patience to configure it right, and it is incredibly easy to do this. I myself haven't gone to the lengths of trying to decrypt or decode any cellular data, but even on windows 7, it wasnt hard to tune to the right frequency, and pick out my own IMSI number from the airwaves, and thats all you need to track someone. My SDR dongle has an effective cellular range of 30 feet, so in essence, I could pick out an IMSI number, and if they are in a moving vehicle, can take a pretty educated guess at which vehicle is emmiting that signal, and effectively track that person. This is incredibly scary.