According to the ACLU, many law enforcement agencies across the U.S. track cell phones as part of their investigations.

Editor’s Note: Amy Gahran writes about mobile tech for She is a San Francisco Bay Area writer and media consultant whose blog,, explores how people communicate in the online age.

Story highlights

ACLU: Phone location tracking is a common tool of police, often without a warrant

Fewer than 5% of agencies say they've never tracked a cell phone's location

Most carriers require a court order to implement cell phone surveillance

Cell phone companies have manuals for police explaining what data they store

CNN  — 

Don’t want the police or your local government to know where you are? Then put your cell phone in airplane mode or turn it off.

Location tracking is inherent in how cell networks function; otherwise nobody’s cell phone would ring. But new evidence from the American Civil Liberties Union shows that phone location tracking has also become a surprisingly common tool of law-enforcement investigations – with, but often without, a warrant.

The ACLU recently obtained records from over 200 police departments and other law enforcement agencies around the U.S. They found that “virtually all” of these agencies track the location of cell phones with data supplied by wireless carriers. (For information on police in your state, check the ACLU’s interactive map, which shows details from responding agencies. Not all states or agencies responded to ACLU’s public-records requests.)

But don’t the police need a warrant for that? It varies by state, but carriers generally say they require a court order to release this data. Regardless of these requirements, however, “Only a tiny minority reported consistently obtaining a warrant and demonstrating probable cause to do so,” said the ACLU.

Not surprisingly, the ACLU disapproves of this practice.

“The government should have to obtain a warrant based upon probable cause before tracking cell phones. That is what is necessary to protect Americans’ privacy, and it is also what is required under the Constitution,” states the ACLU on its site.

Why would police wa