The state of Maryland claims it has the right to track you without a warrant whenever you turn on your phone or make a call. The attorney general there even made that argument in a friend-of-the-court brief.
The case involved a person named Kerron Andrews who was tracked by police using a StingRay, a device which tricks phones into thinking it is a cell tower. Andrews was tracked without a warrant.
“While cell phones are ubiquitous, they all come with ‘off’ switches. Because Andrews chose to keep his cell phone on, he was voluntarily sharing the location of his cell phone with third parties,” states a brief filed by state Attorney General Brian E. Frosh in a case called State of Maryland vs. Kerron Andrews.
Frosh’s claim that citizens give up their Fourth Amendment right against warrantless eavesdropping, simply by switching on their phones, has received plenty of pushback.