Your cellphone isn't just good for texting friends, playing Flappy Bird, listening to music, checking the weather, and ignoring your mother's calls (you assigned her number Darth Vader's theme music, right?). It's also a very efficient tracking beacon for following your movements from place to place. Now, that's multitasking!

It's especially efficient when cops don't go through the hassle of getting a warrant before following your daily routine. But pleasingly paperwork-free though that approach may be for police departments, it's more than a bit creepy. The American Civil Liberties Union (ACLU) argues that it's also unconstitutional, in a Florida case now before the 11th Circuit Court of Appeals.

In terms of the details of the case, the ACLU presents a handy summary:

In 2010, the government obtained four people's cellphone location records over a 67-day period in a criminal investigation in Florida, without a warrant. For one suspect, Quartavious Davis, police got 11,606 location records—an average of 173 location points each day. After Mr. Davis was convicted at trial based substantially on the cellphone location evidence, he appealed to the Eleventh Circuit Court of Appeals. The ACLU, along with the ACLU of Florida, Center for Democracy & Technology, Electronic Frontier Foundation, and National Association of Criminal Defense Lawyers, has filed an amicus brief arguing that the government violated the Fourth Amendment when it obtained Mr. Davis's location records from his wireless carrier without a warrant.

Think about the details of your life the location of your cellphone can open to scrutiny. Do you want each and every place you've been to be trackable through casual scrutiny, with no burden of proof required?

"Your cellphone location records can reveal extraordinarily private information about you, including where you go to the doctor, who your friends are, and where you sleep at night," Nathan Freed Wessler, staff attorney with the ACLU Speech, Privacy, and Technology Project, told the court.

Hell. Keeping where you sleep at night private is half the reason you screen your calls to begin with.

Along those lines, the amicus brief argues that "Americans have a reasonable expectation that they will not be subject to long-term and constant surveillance of their movements."

So, if the cops want to know where you've been, they should have to satisfy Fourth Amendment requirements for getting a warrant.

Ron Bailey reported in December that following your cellphone has become a popular law enforcement pastime.